bash

# 1) (claude code) add time, space complexity to java class
claude

/add-time-space BinarySearch
/add-time-space BFS

# ....

Resource

LC classics problems
- Blind Curated 75
- Grind 75
- Grind 169
- leetcode wiki repo
- leetcode wiki
- LC 官神Github題目分類整理
- LC top 100 likes
- neetcode 150 LC list
  - My Brain after 569 Leetcode Problems
- jiakaobo LC : LC code & video
- LC pattern @ blind : Curated-List-of-Top-100-LeetCode-Questions-to-Save-Your-Time
- LC Algorithm Problem Classification
- cheatsheet-leetcode-a4
- 14-patterns-to-ace-any-coding-interview-question
- grokking-the-coding-interview
LC experiences
- LC難度表
  - 數字越高, 題目越難, 挑與自己LC排名接近的題庫
  - (e.g. LC rank ~= 1600, pick 1600 problem)
- 代碼隨想錄
- Leetcode cookbook
- fucking-algorithm
- fucking-algorithm website
- FAANG 面試準備經驗與建議（一）
- FAANG 面試準備經驗與建議（二）
- LC 小知識
- Meta SWE isnterview prep
- 0到100的軟體工程師面試之路
- 來和大家聊聊我是如何刷題的 : pt1, pt2, pt3
LC Flow
- high level idea : data structure, algorithm
- offer time & space complexity
- code implementation
- offer test case (consider edge case)
- discussion & follow up

Resource.md - Resource for coding interview (keep updating)
Teach yourself CS
MindMapCodeInterview - Mind map for coding interview
CodeInterviewCheatsheet - Coding interview cheetsheet
repl.it - Coding online!

Visualization
- Algorithms viz
- visualgo - DFS / BFS - DFS, BFS visualization
- visualgo - linkedlist - Linkedlist visualization
- visualgo - BST - binary search tree visualization
- toptal-sorting-algorithms- sorting algorithms online

How to: Work at Google — Example Coding/Engineering Interview
bit_manipulation.md - Bit Manipulation Cheat Sheet
Py TimeComplexity - Py basic data structure Time Complexity ref
Py data model - Python data model doc
pgexercises - Postgre exercises
sqlservertutorial
Books
freecodecamp - data-structures
LC interview-experience
Cheatsheet

Data structure
- py core data structure interview
System design
- system_design readme
- sys_design_resource
Tools
LC SQL resources
- LC SQL resource

Progress

Note tags

The Note column of every problem table carries three kinds of tag, all written by script/fix_readme_tags.py from vendored data — so fix the data, not the row:

Tag	Means	Source
`array`, `dp`, `two pointers`, …	the technique the row is filed under, plus LeetCode’s own topics for it	`data/lc_topic_tags.json`
`fb`, `amazon`, `apple`, `netflix`, `google` (FAANG), plus `microsoft`, `uber`, `linkedin`, `bloomberg`	companies known to ask it	`data/company_lc_tags.json`
`blind75`, `neetcode150`, `neetcode250`, `top100liked`	the curated lists it sits on	`data/problem_lists.json`

The three NeetCode lists nest, so a row names only the narrowest one it is on: blind75 already implies NeetCode 150 and 250, and neetcode150 implies 250. top100liked is LeetCode’s own list and cuts across all three, so it stands on its own. NeetCode’s full 972-problem catalogue is deliberately not tagged — it would mark 607 rows without saying which to do first.

bash

python3 script/fix_readme_tags.py --report   # what would change
python3 script/fix_readme_tags.py            # rewrite the Note column

Data Structure

Title	Solution	Use case	Comment	Status
`Linear`
Array	Py			AGAIN*
Queue	Py (array), Py (linkedlist), JS			AGAIN*
Stack	Py, JS (linkedlist), JS (array)			OK
Hash table	Py, JS	usually for improving `time complexity B(O)` via extra space complexity (time-space tradeoff)	`good basic`	AGAIN****
`Linear, Pointer`
LinkedList	Py, JS, Java			OK**
Doubly LinkedList	Python, JS			AGAIN
`Non Linear, Pointer`
Tree	Py			AGAIN**
Binary search Tree (BST)	Python, JS, Java			AGAIN
Binary Tree	Py			AGAIN**
Trie	Py			AGAIN
Heap	heap.py, MinHeap.py, MaxHeap.py, MinHeap.java, MaxHeap.java			AGAIN
Priority Queue (PQ)	Py 1, Py 2, Py 3			AGAIN
`Graph`
Graph	Py, JS. Java1, Java2			OK***
DirectedEdge	Java			AGAIN

Algorithm

Title	Solution	Use case	Comment	Time complexity	Space complexity	Status
Binary search	Python	complexity ref	`Best : O(1), Avg : O(log N), Worst : O(log N)`			AGAIN
Linear search	Python					AGAIN
Breadth-first search (BFS)	Python	`FIND SHORTEST PATH`				AGAIN***
Depth-first search (DFS)	Python	`TO CHECK IF SOMETHING EXIST`	`inorder`, `postorder`, `postorder (can recreate a tree)`	Adjacency List: `O(V+E)`, Adjacency Matrix: `O(V^2)`	`O(V)` (V:Vertices, E:Edges)	AGAIN***
Bubble sort	Python					OK* (3)
Insertion sort	Python, InsertionSort.java	`stable` sort	work very fast for `nearly sorted` array	`Best :O(n), Average : O(n^2), Worst : O(n^2)`	Worst : O(1)	AGAIN
Bucket sort	Python, BucketSort.java					AGAIN
Quick sort	quick_sort.py, quick_sort_v2.py, QuickSort.java, QuickSortV2.java, QuickSortV3.java	NOTE !!!, `avg is NLogN, worst is N**2`, big O ref, big O ref 2	`Best : O(N Log N), Avg : O(N Log N), Worst : O(N^2)`			AGAIN***
Heap sort	Python	big O ref	`Best : O(N Log N), Avg : O(N Log N), Worst : O(N Log N)`			AGAIN**
Merge sort	merge_sort.py, merge_sort_topdown.py, mergesort_bottomup.py, MergeSortTopDown.java, MergeSort.java SQL			`Best : O(N Log N), Avg : O(N Log N), Worst : O(N Log N)`	O(N)	OK* (2)
Pancake sort	Python					AGAIN
Selection sort	Python, JS					AGAIN
Topological sort	Python, Java, Java V2		Topological Sort is a algorithm can find “ordering” on an “order dependency” graph			AGAIN
md5	Python					AGAIN
Union Find	Python 1, Python 2, Java 1, Java 2, Java 3					AGAIN
Dynamic programming	JS 1, fibonacci_dp JS					AGAIN
Dijkstra	Python,Java 1, Java 2					AGAIN***
Floyd-Warshall	Python, Java 1, Java 2				LC 2642	not start
Bellman-Ford	Python					not start
Quick Find	Python, Java	init : O(N), union : O(N), find : O(1)	simple, but slow			AGAIN
Quick Union	Java, Java v2	init : O(N), union : O(N), find : O(N)	lazy approach, route compression, optimized Quick Find			AGAIN
Quick Union (Improvements)			lazy approach, path compression			AGAIN
Priority Queue (`unsorted`)	Java					AGAIN
LRU cache	Python		LC 146			AGAIN
LFU Cache	Python		LC 460			AGAIN
DifferenceArray	Java		LC 1109, 370			AGAIN
Kadane Algo	Java		LC 53, 152,918			AGAIN
Patience sorting (LIS)	Python	`longest increasing subsequence in O(N log N)`, longest chainable run	cheatsheet, the pile count is the LIS length (Dilworth), LC 300, 334, 354, 1964, 1713	O(N log N)	O(N)	not start

Array

#	Title	Solution	Time	Space	Difficulty	Note	Status
0004	Median of Two Sorted Arrays	Python, Java	O(log(min(m, n)))	O(1)	Hard	binary search, binary search on partition, median, heapq (brute), `amazon`, `google`, `apple`, `fb`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN* (1)
0010	Regular Expression Matching	Python, Java	O(m n)*	O(m n)*	Hard	dp, recursion, 2D dp, LC 44, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`	AGAIN (not start)
0015	3 Sum	Python, Java	O(n^2)	O(1)	Medium	two pointers, good basic, check with `# 001 Two Sum`, `#018 4 sum`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	OK******* (7)
0016	3 Sum Closest	Python, Java	O(n^2)	O(1)	Medium	two pointers, `basic`, `good trick`, `3 sum`, `google`, `fb`, `apple`, `microsoft`, `goldman sachs`, `amazon`, `uber`, `bloomberg`	AGAIN******* (3)
0018	4 Sum	Python, Java	O(n^3)	O(1)	Medium	two pointers, `k sum`, check `#016 3 sum`, `# 454 4 SUM II`, good trick, `fb`, `google`, `amazon`, `apple`, `microsoft`, `neetcode250`	AGAIN******** (4)
0026	Remove Duplicates from Sorted Array	Python, Scala, Java	O(n)	O(1)	Easy	two pointers, MUST, `basic`, `good trick`, `microsoft`, `fb`, `google`, `amazon`, `apple`, `uber`, `neetcode250`	AGAIN************** (11)
0027	Remove Element	Python, Java	O(n)	O(1)	Easy	two pointers, MUST, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `neetcode250`	AGAIN****** (2)(MUST)
0031	Next Permutation	Python, Scala, Java	O(n)	O(1)	Medium	array, good trick, 2 pointers, `uber`, `goldman sachs`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`, `top100liked`	AGAIN****************** (9) (MUST)
0041	First Missing Positive	Python, Java	O(n)	O(1)	Hard	array, good trick, hash key, `amazon`, `fb`, `google`, `apple`, `uber`, `microsoft`, `bloomberg`, `neetcode250`, `top100liked`	OK** (2)
0048	Rotate Image	Python, Java	O(n^2)	O(1)	Medium	array, `basic`, `i, j->j, i` `transpose matrix`, `garena`, `amazon`, `apple`, `google`, `fb`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	AGAIN************* (5) (MUST)
0054	Spiral Matrix	Python, Java	O(m n)*	O(1)	Medium	array, good basic, array boundary, matrix, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN**** (4)
0056	Merge Intervals	Python, Java	O(nlogn)	O(n)	Medium	interval, `good trick`, 057 Insert Interval, `twitter`, `microsoft`, `uber`, `google`, `amazon`, `fb`, `apple`, `linkedin`, `bloomberg`, `blind75`, `top100liked`, `netflix`	OK********* (6) (but AGAIN)
0057	Insert Interval	Python, Java	O(n)	O(n)	Medium	interval, good basic, `056 Merge Intervals`, java array, list basic, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `blind75`	AGAIN********** (5) (MUST!)
0059	Spiral Matrix II	Python, Java	O(n^2)	O(1)	Medium	array, check `# 054 Spiral Matrix`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN** (2)
0066	Plus One	Python, Java	O(n)	O(1)	Easy	array, `basic`, `digit`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `neetcode150`	AGAIN** (3)
0073	Set Matrix Zeroes	Python, Java	O(m n)*	O(1)	Medium	array, `matrix`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `blind75`, `top100liked`	OK* (4)
0080	Remove Duplicates from Sorted Array II	Python, Java	O(n)	O(1)	Medium	array, `two pointers`, AGAIN, `basic`, `trick`, `fb`, `#26 Remove Duplicates from Sorted Array`, `google`, `amazon`, `apple`, `microsoft`	AGAIN************ (8)
0118	Pascal’s Triangle	Python, Java	O(n^2)	O(1) excluding output	Easy	array, `trick`, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `top100liked`	AGAIN** (2)
0119	Pascal’s Triangle II	Python, Java	O(n^2)	O(n)	Easy	array, check with `# 118 Pascal's Triangle`, `amazon`, `google`, `microsoft`	OK** (4)
0121	Best Time to Buy and Sell Stock	Python, Java	O(n)	O(1)	Easy	array, `dp`, `basic`, `greedy`, `uber`, `microsoft`, `amazon`, `fb`, `google`, `apple`, `bloomberg`, `blind75`, `top100liked`	OK****** (7) (but again)
0157	Read N Characters Given Read4	Python, Java	O(n)	O(1)	Easy	array, 🔒, buffer, `google`, `amazon`, `fb`, `microsoft`	AGAIN**** (3)
0163	Missing Ranges	Python, Java	O(n)	O(1)	Medium	array, two pointer, 🔒, `google`, `amazon`, `fb`	OK******* (4)
0169	Majority Element	Python, Java	O(n)	O(1)	Easy	array, Boyer-Moore majority vote, LC 229, `basic`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `neetcode250`, `top100liked`	OK*
0189	Rotate Array	Python, Java	O(n)	O(1)	Medium	array, k % len(nums), good basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`, `neetcode250`, `top100liked`	OK* (7) (but again)
0209	Minimum Size Subarray Sum	Python, Java	O(n)	O(1)	Medium	array, good basic, sliding window, `Binary Search`, `trick`, `2 pointers`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`	OK********** (7) (but again)
0215	Kth Largest Element in an Array	Python, Java	O(n) ~ O(n^2)	O(1)	Medium	array, EPI, `quick sort`, bubble sort, sort, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`	OK* (2)
0228	Summary Ranges	Python, Java	O(n)	O(1)	Easy	array, check `# 163 Missing Ranges`, `good basic`, `google`, `amazon`, `fb`, `microsoft`, `uber`	OK********* (5)
0229	Majority Element II	Python, Java	O(n)	O(1)	Medium	array, Boyer-Moore majority vote (2 candidates), LC 169, `good trick`, `amazon`, `google`, `apple`, `microsoft`, `bloomberg`, `neetcode250`	OK
0238	Product of Array Except Self	Python, Java	O(n)	O(1)	Medium	array, left, right array, LintCode, `good trick`, `apple`, `microsoft`, `amazon`, `fb`, `google`, `uber`, `linkedin`, `blind75`, `top100liked`	OK******* (but again)(6)
0240	Search a 2D Matrix II	Python, Java	O(m + n)	O(1)	Medium	array, LintCode, `basic`, `matrix`, `trick`, `binary search`, check `# 74 Search a 2D Matrix`, `amazon`, `apple`, `google`, `fb`, `microsoft`, `uber`, `top100liked`	OK***** (7) (but again)
0243	Shortest Word Distance	Python, Java	O(n)	O(1)	Easy	array, 🔒, `basic`, `google`, `amazon`, `microsoft`, `uber`, `linkedin`	OK*
0245	Shortest Word Distance III	Python, Java	O(n)	O(1)	Medium	array, 🔒, check `Shortest Word Distance I II III`, `google`, `apple`, `microsoft`, `linkedin`	OK*
0251	Flatten 2D Vector	Python, Java	ctor: O(1), next: O(1) amortized	O(1)	Medium	design, 🔒, `good basic`, check`# 341 Flatten Nested List Iterator`, `google`, `airbnb`, `twitter`, `amazon`, `fb`, `apple`, `uber`	AGAIN******** (5)
0277	Find the Celebrity	Python, Java	O(n)	O(1)	Medium	array, graph, 🔒, `fb`, `amazon`, `trick`, `two pointers`, `interactive`, `google`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN********** (5)
0287	Find the Duplicate Number	Python, Java	O(n)	O(1)	Medium	two pointers, good trick, Floyd cycle detection, binary search on value, check `# 142 Linked List Cycle II`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	OK* (2)
0289	Game of Life	Python, Java	O(m n)*	O(1)	Medium	array, simultaneous, matrix, `complex`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN*** (4)
0293	Flip Game	Python, Java	O(n^2)	O(n)	Easy	array, 🔒, `basic`, `string`, `google`	AGAIN*
0308	Range Sum Query 2D - Mutable	Python, Java	ctor: O(m n), update: O(logm * logn), query: O(logm * logn)*	O(m n)*	Hard	array, LC 303, LC 304, pre-sum, binary indexed tree (BIT), segment tree, 🔒, `google`, `fb`	AGAIN(1)***** not start
0311	Sparse Matrix Multiplication	Python, Java	O(m n * l)*	O(m l)*	Medium	array, 🔒, matrix, `basic`, `fb`, `google`, `amazon`, `apple`, `linkedin`	OK**** (5)
0334	Increasing Triplet Subsequence	Python, Java	O(n)	O(1)	Medium	array, AGAIN, check LC 300, `trick`, `fb`, `google`, `amazon`, `uber`	OK***** (but again) (4)
0335	Self Crossing	Java	O(n)	O(1)	Hard	array, geometry, `google`, `amazon`	Again (not start)
0370	Range Addition	Python, Java	O(k + n)	O(n)	Medium	prefix sum, prefix, diff array, check `# 598 Range Addition II`, `amazon`, LC 1109, LC 1094, `google`	AGAIN************** (4) (MUST)
0384	Shuffle an Array	Python, Java	ctor: O(n), shuffle: O(n)	O(n)	Medium	design, EPI, `trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`	OK*
0396	Rotate Function	Python, Java	O(n)	O(1)	Medium	array, can pass, math, `trick`, `amazon`, `google`, `apple`	AGAIN*** (3)
0412	Fizz Buzz	Python, Scala, Java	O(n)	O(1)	Easy	array, `basic`, string, simulation, LC 1195, `math`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `linkedin`	OK
0414	Third Maximum Number	Python, Java	O(n)	O(1)	Easy	array, `good basic`, `amazon`, `google`, `fb`, `apple`, `microsoft`	OK* (4)
0419	Battleships in a Board	Python, Java	O(m n)*	O(1)	Medium	array, `matrix`, count only top-left cell of each ship, no extra space, LC 200, `amazon`, `google`, `fb`, `apple`, `microsoft`	AGAIN*
0422	Valid Word Square	Python, Java	O(m n)*	O(1)	Easy	array, 🔒, `basic`, `matrix`, `google`	AGAIN*
0442	Find All Duplicates in an Array	Python, Java	O(n)	O(1)	Medium	array, index-as-hash (negative marking), LC 448, LC 41, `good trick`, `amazon`, `google`, `fb`, `apple`, `microsoft`	OK*
0448	Find All Numbers Disappeared in an Array	Python, Java	O(n)	O(1)	Easy	array, index-as-hash (negative marking), LC 442, LC 41, `good basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK
0498	Diagonal Traverse	Python, Java	O(m n)*	O(1) excluding output	Medium	array, `matrix`, Diagonal, `google`, `fb`, `amazon`, `apple`, `microsoft`	AGAIN****** (5)
0531	Lonely Pixel I	Python, Java	O(m n)*	O(m + n)	Medium	array, 🔒, `matrix`, `basic`, `google`, `microsoft`	AGAIN*
0533	Lonely Pixel II	Python, Java	O(m n)*	O(m n)*	Medium	array, 🔒, `matrix`, row-pattern hashing, LC 531, `google`	AGAIN (not start*)
0565	Array Nesting	Python, Java	O(n)	O(1)	Medium	array, `union find`, `dfs`, `apple`, `google`	AGAIN**** (1)
0566	Reshape the Matrix	Python, Java	O(m n)*	O(m n)*	Easy	array, `basic`, `matrix`, `fb`	AGAIN**
0581	Shortest Unsorted Continuous Subarray	Python, Java	O(n)	O(1)	Easy	array, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN*
0605	Can Place Flowers	Python, Java	O(n)	O(1)	Easy	array, `pass vs continue`, `amazon`, `fb`, `apple`, `microsoft`, `linkedin`	OK*
0624	Maximum Distance in Arrays	Python, Java	O(n)	O(1)	Easy	array, 🔒, track running max excluding the current array, `good trick`	AGAIN*
0643	Maximum Average Subarray I	Python, Java	O(n)	O(1)	Easy	array, `Math`, `basic`, `google`, `amazon`, `fb`	AGAIN*
0661	Image Smoother	Python, Java	O(m n)*	O(m n)*	Easy	array, `matrix`, `basic`, `amazon`, `fb`, `apple`, `microsoft`	OK***** (4) (but again!)
0665	Non-decreasing Array	Python, Java	O(n)	O(1)	Easy	array, `greedy`, at most one modification, decide nums[i-1] vs nums[i+1], `good trick`, `google`, `amazon`, `fb`	AGAIN (not start)
0667	Beautiful Arrangement II	Python, Java	O(n)	O(1)	Medium	array, `math`, construct k distinct diffs then run out, `trick`, `google`	AGAIN (not start)
0670	Maximum Swap	Python, Java	O(n)	O(n)	Medium	array, `good basic`, n = number of digits, last-occurrence index, string + pointers, `fb`, `math`, `greedy`, `google`, `amazon`, `apple`, `microsoft`	AGAIN************ (9) (MUST)
0674	Longest Continuous Increasing Subsequence	Python, Java	O(n)	O(1)	Easy	array, `good basic`, `dp`, `2 pointers`, `fb`, `google`, `amazon`, `apple`, `microsoft`	OK*** (5)
0697	Degree of an Array	Python, Java	O(n)	O(n)	Easy	array, `hash table`, degree + first/last index, `good basic`	AGAIN (not start)
0713	Subarray Product Less Than K	Python, Java	O(n)	O(1)	Medium	array, `basic`, `sliding window`, good trick, `google`, `amazon`, `fb`, `microsoft`	OK****** (3) (but again)
0717	1-bit and 2-bit Characters	Python, Java	O(n)	O(1)	Easy	array, Greedy, `google`, `amazon`, `apple`	AGAIN (not start)
0723	Candy Crush	Python, Java	O((R C)^2)*	O(1)	Medium	array, `complex`, `google`, `fb`, `uber`, `bloomberg`	AGAIN (not start)
0724	Find Pivot Index	Python, Java	O(n)	O(1)	Easy	array, good basic, prefix-sum, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	OK**** (2)
0729	My Calendar I	Python, Java	O(nlogn)	O(n)	Medium	array, good basic, interval, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN**** (1)
0731	My Calendar II	Python, Java	O(n^2)	O(n)	Medium	array, `trick`, good trick, scanning line, `google`, `amazon`, `microsoft`	AGAIN******** (4)
0747	Largest Number At Least Twice of Others	Python, Java	O(n)	O(1)	Easy	array, `good basic`, `data structure`, `google`	OK*
0755	Pour Water	Python, Java	O(v n)*	O(1)	Medium	array, `complex`	AGAIN (not start)
0759	Employee Free Time	Python, Java	O(nlogn)	O(n)	Hard	interval, LC 56 and LC 986, heap, merger intervals, scanning line, `amazon`, `fb`, `google`, `uber`, `airbnb`, `apple`, `microsoft`	AGAIN********** (2) (not start)
0766	Toeplitz Matrix	Python, Java	O(m n)*	O(1)	Easy	array, `basic`, `matrix`, `google`, `amazon`, `fb`, `apple`	AGAIN* (2)
0769	Max Chunks To Make Sorted	Python, Java	O(n)	O(1)	Medium	prefix sum, LC 768, good trick, stack, array, `google`, `greedy`, `amazon`, `microsoft`, `uber`	AGAIN*** (2)
0792	Number of Matching Subsequences	Python, Java	O(n + w)	O(w)	Medium	hash table, basic, hash map, `google`, `amazon`, `fb`, `apple`	AGAIN**** (2)
0794	Valid Tic-Tac-Toe State	Python, Java	O(1)	O(1)	Medium	array, `complex`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN
0795	Number of Subarrays with Bounded Maximum	Python, Java	O(n)	O(1)	Medium	array, count subarrays with max in [left, right], `two pointers`, `trick`, `google`, `amazon`, `apple`, `microsoft`	AGAIN (not start*)
0807	Max Increase to Keep City Skyline	Python, Java	O(n^2)	O(n)	Medium	array, `matrix`, row max + col max, `greedy`, `good basic`, `google`, `amazon`	AGAIN*
0821	Shortest Distance to a Character	Python, Java	O(n)	O(1) excluding output	Easy	array, `basic`, `trick`, `google`, `apple`	AGAIN**
0830	Positions of Large Groups	Python, Java	O(n)	O(1)	Easy	array, `basic`, `string`, `google`	AGAIN*
0832	Flipping an Image	Python, Java	O(n^2)	O(1)	Easy	array, `matrix`, reverse each row then invert, `two pointers`, `basic`, `google`, `fb`	AGAIN*
0835	Image Overlap	Python, Java	O(n^4)	O(n^2)	Medium	array, `matrix`, brute-force all shifts, count overlaps with a delta hashmap, `google`	AGAIN (not start)
0840	Magic Squares In Grid	Python, Java	O(m n)*	O(1)	Easy	array, `complex`, `google`	AGAIN (not start)
0842	Split Array into Fibonacci Sequence	Python, Java	O(n^3)	O(n)	Medium	array, check `# 306 Addictive Number`, `basic`, `dfs`, `fibonacci`, `string`, `backtracking`, `amazon`	AGAIN* (not start)
0845	Longest Mountain in Array	Python, Java	O(n)	O(1)	Medium	array, `basic`, 2 pointers expansion, `google`, `amazon`	AGAIN************ (2)(MUST)
0849	Maximize Distance to Closest Person	Python, Java	O(n)	O(1)	Medium	array, `basic`, 2 pointers, LC 855, `google`, `amazon`, `microsoft`	AGAIN********* (2)
0860	Lemonade Change	Python, Java	O(n)	O(1)	Easy	array, `amazon`, `apple`, `neetcode250`	OK* (2)
0868	Transpose Matrix	Python, Java	O(r c)*	O(r c)*	Easy	array, `basic`, `bit manipulation`	OK*
0885	Spiral Matrix III	Python, Java	O(max(m, n)^2)	O(1)	Medium	array, `basic`, `fb`	AGAIN* (not start)
0888	Fair Candy Swap	Python, Java	O(m + n)	O(m + n)	Easy	array, `basic`, `trick`, `amazon`, `uber`	OK*
0896	Monotonic Array	Python, Java	O(n)	O(1)	Easy	array, `all`, `fb`, `amazon`	OK
0905	Sort Array By Parity	Python, Java	O(n)	O(1)	Easy	array, custom sort, 2 pointers, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN***** (1)(MUST)
0909	Snakes and Ladders	Python, Java	O(n^2)	O(n^2)	Medium	array, matrix, bfs, `complex`, `amazon`, `google`, `apple`, `microsoft`, `uber`	AGAIN***** (3)
0915	Partition Array into Disjoint Intervals	Python, Java	O(n)	O(n)	Medium	array, `basic`, `trick`, `amazon`, `microsoft`	AGAIN* (not start)
0918	Maximum Sum Circular Subarray	Python, Java	O(n)	O(1)	Medium	array, check `# 053 Maximum Subarray`, `basic`, `trick`, `google`, `amazon`, `fb`, `uber`, `neetcode250`	AGAIN** (2)
0921	Minimum Add to Make Parentheses Valid	Python, Java	O(n)	O(1)	Medium	array, `basic`, `trick`, `string`, `stack`, `greedy`, `amazon`, `fb`, `microsoft`	AGAIN**
0922	Sort Array By Parity II	Python, Java	O(n)	O(1)	Easy	array, `basic`, `amazon`, `microsoft`	AGAIN*
0923	3Sum With Multiplicity	Python, Java	O(n^2)	O(n)	Medium	array, LC 15, count pairs with a Counter, combination math, `trick`	AGAIN (not start)
0932	Beautiful Array	Python, Java	O(nlogn)	O(n)	Medium	array, divide and conquer, odd/even split, `trick`, `google`, `fb`	AGAIN** (not start) (1)
0941	Valid Mountain Array	Python, Java	O(n)	O(1)	Easy	array, `basic`, `good basic`, `google`, `amazon`, `uber`	AGAIN*
0945	Minimum Increment to Make Array Unique	Python, Java	O(nlogn)	O(n)	Medium	array, `trick`, `good`, `uber`	AGAIN**
0947	Most Stones Removed with Same Row or Column	Python, Java	O(n a(n))*	O(n)	Medium	array, Union Find on row/col keys, dfs, `trick`, `google`, `hash table`, `amazon`, `apple`, `uber`	AGAIN** (1) (not start)
0949	Largest Time for Given Digits	Python, Java	O(1)	O(1)	Easy	array, brute force all 4! digit permutations, `math`, `basic`, `google`, `amazon`	OK*
0950	Reveal Cards In Increasing Order	Python, Java	O(nlogn)	O(n)	Medium	array, sort + deque simulation, queue, 2 pointers, `google`, `amazon`	AGAIN (not start) (2)
0954	Array of Doubled Pairs	Python, Java	O(n + klogk)	O(k)	Medium	array, `counter`, `dict`, `trick`, `google`, `amazon`, `uber`	AGAIN**
0961	N-Repeated Element in Size 2N Array	Python, Java	O(n)	O(1)	Easy	array, LC 217, hash table / count, `basic`, `apple`	OK
0989	Add to Array-Form of Integer	Python, Java	O(n)	O(1)	Easy	array, add xxx to sum, `fb`, `google`	AGAIN (not start)
1007	Minimum Domino Rotations For Equal Row	Java	O(n)	O(1)	Medium	array, `google`, dp, `amazon`, `apple`	AGAIN (1)
1014	Best Sightseeing Pair	Python, Java	O(n)	O(1)	Medium	array, dp, good basic, Spotify, `google`	AGAIN (not start)
1027	Longest Arithmetic Subsequence	Python, Java	O(n^2)	O(n^2)	Medium	array, dp, hash table, trick, `google`, `amazon`, `fb`, `microsoft`, `uber`	AGAIN*** (not start)
1031	Maximum Sum of Two Non-Overlapping Subarrays	Python, Java	O(n)	O(n)	Medium	array, prefix sum+slide window, good trick, `google`, `amazon`, `fb`	AGAIN*************** (3)(MUST)
1041	Robot Bounded In Circle	Python, Java	O(n)	O(1)	Medium	array, math, `amazon`, `string`, `simulation`, `google`, `apple`, `microsoft`	AGAIN** (2)
1074	Number of Submatrices That Sum to Target	Java	O(m^2 n)*	O(n)	Hard	array, hashmap, prefix sum, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
1089	Duplicate Zeros	Java	O(n)	O(1)	Easy	array, `two pointers`, in-place shift from the back, `good trick`, `google`, `amazon`, `microsoft`	AGAIN (not start)
1094	Car Pooling	Python, Java	O(n + k)	O(k)	Medium	array, range addition, prefix sum, LC 370, `google`, `amazon`, `fb`, `microsoft`, `neetcode250`	AGAIN********** (5) (MUST)
1109	Corporate Flight Bookings	Python, Java	O(n + k)	O(n)	Medium	array, LC 370, difference array, good basic, `amazon`, `google`	AGAIN********* (MUST) (3)
1248	Count Number of Nice Subarrays	Python, Java	O(n)	O(n)	Medium	array, LC 828, map, Prefix sum, exactly K with at most K, `amazon`	AGAIN********************* (4) (MUST)
1272	Remove Interval	Java	O(n)	O(n)	Medium	array, `google`	AGAIN (not start)
1275	Find Winner on a Tic Tac Toe Game	Python, Java	O(1)	O(1)	Easy	array, `amazon`, `google`, `fb`, `apple`, `microsoft`	AGAIN (not start)
1288	Remove Covered Intervals	Java	O(nlogn)	O(1)	Medium	array, greedy, interval, `amazon`, `fb`, `apple`	AGAIN (not start)
1314	Matrix Block Sum	Java	O(m n)*	O(m n)*	Medium	array, prefix sum, dp, matrix sum, `google`, `amazon`, `fb`, `apple`	AGAIN (not start)
1431	Kids With the Greatest Number of Candies	Java	O(n)	O(1) excluding output	Easy	array, compare each candy count with the max, `basic`, `google`, `amazon`, `uber`	AGAIN (not start)
1470	Shuffle the Array	Java	O(n)	O(1) excluding output	Easy	array, index mapping, 2 pointers, `basic`, `google`, `amazon`, `apple`, `uber`	AGAIN (not start)
1564	Put Boxes Into the Warehouse I	Java	O(nlogn)	O(m)	Medium	array, `google`	AGAIN (not start)
1567	Maximum Length of Subarray With Positive Product	Python, Java	O(n)	O(1)	Medium	array, good trick, dp, 2 pointers, `amazon`, `microsoft`	AGAIN**** (1) (not start)
1672	Richest Customer Wealth	Java	O(m n)*	O(1)	Easy	array, row sum then max, `matrix`, `basic`, `google`, `amazon`, `apple`, `uber`	OK
1806	Minimum Number of Operations to Reinitialize a Permutation	Java	O(n)	O(n)	Medium	array, brute force, `google`	AGAIN (not start)
1914	Cyclically Rotating a Grid	Python, Java	O(m n)*	O(m n)*	Medium	array, brute force, dequeue`amazon`, `amazon`	AGAIN (not start)
1920	Build Array from Permutation	Java	O(n)	O(1) excluding output	Easy	array, index mapping, `basic`, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN (not start)
1929	Concatenation of Array	Java	O(n)	O(1) excluding output	Easy	array, concatenate, `basic`, `google`, `neetcode250`	AGAIN (not start)
1991	Find the Middle Index in Array	Java	O(n)	O(1)	Easy	array, prefix sum, LC 724, `good basic`	AGAIN (not start)
2033	Minimum Operations to Make a Uni-Value Grid	Python	O(m n * log(m * n))*	O(m n)*	Medium	array, feasible iff all values agree mod x, median minimizes sum of abs deviation, sort, math, LC weekly	AGAIN(1)
2079	Watering Plants	Java	O(n)	O(1)	Medium	array, `google`	AGAIN (not start)
2553	Separate the Digits in an Array	Java	O(n d)*	O(1) excluding output	Easy	array, weekly 97	OK
2640	Find the Score of All Prefixes of an Array	Java	O(n)	O(1) excluding output	Medium	array, lc weekly 102	OK (1)
2644	Find the Maximum Divisibility Score	Java	O(n m)*	O(1)	Easy	array, sort	Again (1)
3195	Find the Minimum Area to Cover All Ones I	Java	O(m n)*	O(1)	Medium	array, LC weekly	AGAIN (1)
3964	Minimum Lights to Illuminate a Road	Python, Java	O(n)	O(n)	Medium	array, diff array, LC bi weekly	AGAIN (1)

Set

#	Title	Solution	Time	Space	Difficulty	Note	Status
1316	Distinct Echo Substrings	Java	O(n^2)	O(n^2)	Hard	set, set of substrings, rolling hash / Rabin-Karp for O(n^2), `trick`, `string`, `trie`, `google`	Again (not start)
1436	Destination City	Java	O(n)	O(n)	Easy	set, set of outgoing cities, find the city with no outgoing path, `basic`, `google`	Again (1)
2357	Make Array Zero by Subtracting Equal Amounts	Java	O(n)	O(n)	Easy	set, count distinct non-zero values, `good trick`	Again (1)
2657	Find the Prefix Common Array of Two Arrays	Java	O(n)	O(n)	Medium	set, frequency array + running common count, good trick, weekly_103	Again**** (1)
2682	Find the Losers of the Circular Game	Java	O(n)	O(n)	Easy	set, simulate the circular jumps until a friend repeats, hashset, `basic`	Again (1)

Slide Window

#	Title	Solution	Time	Space	Difficulty	Note	Status
0030	Substring with Concatenation of All Words	Java	O(n l)*	O(m l)*	Hard	sliding window, hashmap word count, fixed-size window of `l` chars, LC 76, `good trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN(not start)
0768	Max Chunks To Make Sorted II	Java	O(n)	O(n)	Hard	sliding window, LC 769, prefix max vs suffix min, monotonic stack, `good trick`, `array`, `greedy`, `google`, `amazon`, `microsoft`	AGAIN(not start)
1004	Max Consecutive Ones III	Java	O(n)	O(1)	Medium	sliding window, longest window with at most k zeros, LC 487, LC 424, `good basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`	Again (1)
1423	Maximum Points You Can Obtain from Cards	Python	O(n)	O(1)	Medium	slide window, window the complement: minimise the block you leave, `good trick`, `google`, `amazon`, `apple`, `uber`	AGAIN(1)
1461	Check If a String Contains All Binary Codes of Size K	Python	O(n)	O(2^k)	Medium	slide window, rolling window as an int + set, pigeonhole early exit, `bit manipulation`, `rolling hash`, `google`	AGAIN(1)
1658	Minimum Operations to Reduce X to Zero	Python, Java	O(n)	O(1)	Medium	sliding window, turn “remove from both ends” into “longest middle subarray with sum total-x”, `good trick`, `google`, `amazon`	AGAIN******** (1)(MUST)
1838	Frequency of the Most Frequent Element	Java, Python	O(nlogn)	O(1)	Medium	sliding window, sort + sliding window with sum, binary search on the answer, `good trick`, `amazon`, `microsoft`	AGAIN******** (1)(good)
1839	Longest Substring Of All Vowels in Order	Python, Java	O(n)	O(1)	Medium	sliding window, window must be non-decreasing and cover all 5 vowels, `basic`	AGAIN** (1)(good)
1888	Minimum Number of Flips to Make The Binary String Alternating	Python	O(n)	O(1)	Medium	slide window, double the string = every rotation, score both alternating targets at once, `good trick`, `google`	AGAIN(1)
2555	Maximize Win From Two Segments	Java	O(n)	O(n)	Medium	sliding window, best window ending at i + best window before i, prefix dp, weekly 97	AGAIN (not start)
2962	Count Subarrays Where Max Element Appears at Least K Times	Java	O(n)	O(1)	Medium	sliding window, count windows containing the max at least k times, `good trick`, weekly 375	AGAIN************ (3)
3090	Maximum Length Substring With Two Occurrences	Java	O(n)	O(1)	Easy	sliding window, longest window where every char appears at most twice, weekly 390	AGAIN (1)

Hash Table

#	Title	Solution	Time	Space	Difficulty	Note	Status
0001	Two Sum	Python, Java,Scala	O(n)	O(n)	Easy	hash table, `good basic`, `apple`, `amazon`, `uber`, `grab`, `fb`, `google`, `microsoft`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK*** (6) (but again)
0003	Longest Substring Without Repeating Characters	Python, Java	O(n)	O(1)	Medium	hash table, 2 pointers, optimized (SLIDING WINDOW + DICT), `good trick`, `hashMap`, MUST, `apple`, `amazon`, `fb`, `google`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	AGAIN**************** (12) (but AGAIN)
0036	Valid Sudoku	Python, Java	O(9^2)	O(9^2)	Medium	hash table, array, hashset, `uber`, `apple`, `amazon`, `google`, `fb`, `microsoft`, `neetcode150`	OK**** (3) (again)
0049	Group Anagrams	Python, Scala, Java	O(n glogg)*	O(n g)*	Medium	hash table, `good basic`, dict, `trick`, `dict + sort`, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `bloomberg`, `blind75`, `top100liked`	OK ********** (6)
0170	Two Sum III - Data structure design	Python , Java	add: O(1), find: O(n)	O(n)	Easy	hash table, 🔒, `trick`, `good basic`, `linkedin`, `fb`	OK*** (4)
0187	Repeated DNA Sequences	Python , Java	O(n)	O(n)	Medium	hash table, `basic`, `trick`, `set`, `linkedin`, `google`, `amazon`, `apple`	AGAIN**
0202	Happy Number	Python , Java	O(k)	O(k)	Easy	hash table, `twitter`, `airbnb`, `uber`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`, `neetcode150`	AGAIN** (4)
0204	Count Primes	Python , Java	O(nloglogn)	O(n)	Medium	hash table, Sieve of Eratosthenes, `good trick`, cache, `microsoft`, `amazon`, `array`, `math`, `number theory`, `google`, `apple`	AGAIN******** (5)
0205	Isomorphic Strings	Python, Java	O(n)	O(1)	Easy	hash table, `basic`, `trick`, `bloomberg`, `google`, `amazon`, `fb`, `apple`, `uber`, `linkedin`	AGAIN**
0217	Contains Duplicate	Python , Java	O(n)	O(n)	Easy	hash table, `yahoo`, `airbnb`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `blind75`	OK
0219	Contains Duplicate II	Python ,Java	O(n)	O(n)	Easy	hash table, `basic`, `trick`, `google`, `amazon`, `fb`, `apple`, `neetcode250`	AGAIN*
0244	Shortest Word Distance II	Python , Java	ctor: O(n), lookup: O(a + b)	O(n)	Medium	hash table, 🔒, `amazon`, `uber`, `linkedin`	AGAIN (not start*)
0246	Strobogrammatic Number	Python, Java	O(n)	O(1)	Easy	hash table, 🔒, `google`, `fb`, `microsoft`	OK* (5)
0249	Group Shifted Strings	Python , Java	O(n l)*	O(n l)*	Medium	hash table, LC 49, 🔒, hashmap, char, `apple`, `uber`, `google`, `amazon`, `fb`	OK *****(6) (but again)
0266	Palindrome Permutation	Python , Java	O(n)	O(1)	Easy	hash table, 🔒, `google`, `amazon`, `fb`, `microsoft`, `uber`, `bloomberg`	OK
0288	Unique Word Abbreviation	Python , Java	ctor: O(n), lookup: O(1)	O(k)	Medium	hash table, 🔒, ?, `google`, `fb`	AGAIN (2)(not start)
0290	Word Pattern	Python , Java	O(n)	O©	Easy	hash table, `basic`, chcek `# 205 Isomorphic Strings`, `good basic`, `for ptn, word in zip(pattern, words)`, `dropbox`, `uber`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN* (3)
0299	Bulls and Cows	Python , Java	O(n)	O(1)	Easy	hash table, `trick`, `map(operator.eq, a, b)`, `amazon`, `airbnb`, `google`	AGAIN* (3)
0314	Binary Tree Vertical Order Traversal	Python , Java	O(n)	O(n)	Medium	hash table, LC 987, 🔒, `BFS`, `DFS`, `tree`, `trick`, `google`, `amazon`, `fb`, `microsoft`, `apple`	OK**** (6)
0325	Maximum Size Subarray Sum Equals k	Python, Java	O(n)	O(n)	Medium	hash table, prefix sum, 🔒, `hashmap`, `good trick`, `dict`, `fb`, `google`, `amazon`, `apple`, `microsoft`	AGAIN***************** (8) (MUST)
0336	Palindrome Pairs	Java	O(n l^2)*	O(n l)*	Hard	hash table, LC 49, Anagrams, string op, hashmap, sub-string, `google`, `amazon`, `fb`, `apple`, `uber`	Again******* (2)(again)
0356	Line Reflection	Python , Java	O(n)	O(n)	Medium	hash table, 🔒, Hash, Two Pointers, `math`, `google`, `amazon`	AGAIN (not start)
0359	Logger Rate Limiter	Python, Java	O(1), amortized	O(k)	Easy	hash table, 🔒, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	OK
0387	First Unique Character in a String	Python , Java	O(n)	O(n)	Easy	hash table, `amazon`, `apple`, `fb`, `google`, `microsoft`, `bloomberg`	OK
0388	Longest Absolute File Path	Python , Java	O(n)	O(d)	Medium	hash table, stack, good trick, file system, `google`, `string`, `dfs`, `amazon`, `fb`, `apple`, `uber`	AGAIN******* (3)
0409	Longest Palindrome	Python , Java	O(n)	O(1)	Easy	hash table, count char pairs, add 1 if any odd count remains, `basic`, `google`, `amazon`	OK*
0424	Longest Repeating Character Replacement	Python, Java	O(n)	O(1)	Medium	hash table, hash map, max_freq, `silding window`, `good trick`, LC blind pattern, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `blind75`	AGAIN**************** (10) (MUST)
0438	Find All Anagrams in a String	Python , Java	O(n)	O(1)	Medium	hash table, `trick`, `AGAIN`, `sliding window`, `acc Counter`, `amazon`, `fb`, `apple`, `google`, `uber`, `yahoo`, `microsoft`, `bloomberg`, `top100liked`	AGAIN************** (11)(must)
0447	Number of Boomerangs	Python , Java	O(n^2)	O(n)	Easy	hash table, `trick`, `google`	AGAIN (3) (not start)
0454	4Sum II	Python , Java	O(n^2)	O(n^2)	Medium	hash table, check LC 018 4SUM, `trick`, `basic`, `amazon`, `google`, `fb`, `apple`, `uber`	AGAIN**
0463	Island Perimeter	Python , Java	O(m n)*	O(1)	Easy	hash table, count cells then subtract shared edges, `matrix`, `basic`, `google`, `fb`, `amazon`, `array`, `dfs`, `bfs`, `apple`, `microsoft`, `bloomberg`, `neetcode250`	AGAIN** (2)
0470	Implement Rand10() Using Rand7()	Python , Java	O(1)	O(1)	Medium	hash table, `trick`, `google`, `math`, `apple`, `microsoft`, `uber`	AGAIN** (3)
0473	Matchsticks to Square	Python , Java	O(n s * 2^n)*	O(n (2^n + s))*	Medium	hash table, good trick, backtrack, `array`, `dp`, `amazon`, `microsoft`, `neetcode250`	AGAIN****** (2)
0523	Continuous Subarray Sum	Python , Java	O(n)	O(k)	Medium	hash table, sub array sum, check `# 560 Subarray Sum Equals K`, `good trick`, `substring`, `AGAIN`, `microsoft`, `fb`, `apple`, `google`, `amazon`	AGAIN*************** (10) (MUST)
0525	Contiguous Array	Python, Java	O(n)	O(n)	Medium	hash table, sub-array sum, LC 560, 525, 974, `good basic`, `array`, `hashmap`, `fb`, `amazon`, `google`, `apple`	AGAIN****************** (12) (MUST)
0532	K-diff Pairs in an Array	Python , Java	O(n)	O(n)	Medium	hash table, `basic`, `collections.Counter()`, `a-b =k -> a = k + b` , `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`	AGAIN********** (6)
0554	Brick Wall	Python , Java	O(n)	O(m)	Medium	hash table, LC 252, gap map, `trick`, `hash map`, `bloomberg`, `fb`, grab, `google`	AGAIN******** (6)
0560	Subarray Sum Equals K	Python, Java	O(n)	O(n)	Medium	hash table, LC 560, 525, 974, prefix sum, `must check`, check `# 523 Continuous Subarray Sum`, LC 1268, `basic`, `substring`, `good trick`, `google`, `fb`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`, `top100liked`	AGAIN***************** (8) (MUST)
0561	Array Partition I	Python , Java	O(nlogn)	O(1)	Easy	hash table, sort then sum every other element, `greedy`, `good trick`, `array`, `amazon`, `apple`	OK
0575	Distribute Candies	Python , Java	O(n)	O(n)	Easy	hash table, min(distinct kinds, n / 2), hashset, `basic`, `microsoft`	OK
0594	Longest Harmonious Subsequence	Python , Java	O(n)	O(n)	Easy	hash table, `basic`, `good trick`	OK* (3)
0599	Minimum Index Sum of Two Lists	Python , Java	O((m + n) l)*	O(m l)*	Easy	hash table, `yelp`, `apple`	OK*
0609	Find Duplicate File in System	Python , Java	O(n l)*	O(n l)*	Medium	hash table, `collections.defaultdict(list)`, `dropbox`, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK*
0657	Robot Return to Origin	Python , Java	O(n)	O(1)	Easy	hash table, `amazon`, `string`, `simulation`, `google`	OK (2)
0710	Random Pick with Blacklist	Java	ctor: O(b), pick: O(1)	O(b)	Hard	hash table, hashmap, `google`, `amazon`, `uber`	AGAIN (not start)
0748	Shortest Completing Word	Python , Java	O(n)	O(1)	Easy	hash table, `collections.Counter`, `google`, `linkedin`	AGAIN* (3)
0760	Find Anagram Mappings	Python , Java	O(n)	O(n)	Easy	hash table, `basic`, `collections.defaultdict`, `google`	OK
0771	Jewels and Stones	Python , Java	O(m + n)	O(n)	Easy	hash table, `amazon`, `google`, `fb`, `apple`, `uber`	OK (2)
0811	Subdomain Visit Count	Python , Java	O(n)	O(n)	Easy	hash table, `indeed`, `bloomberg`, `google`, `amazon`	AGAIN (not start)
0822	Card Flipping Game	Python , Java	O(n)	O(n)	Medium	hash table, `good basic`	AGAIN* (3)
0825	Friends Of Appropriate Ages	Python , Java	O(a^2 + n)	O(a)	Medium	hash table, `good basic`, `counter`, `AGAIN`, `fb`, `array`, `two pointers`, `binary search`	AGAIN***** (5)
0869	Reordered Power of 2	Python , Java	O(1)	O(1)	Medium	hash table, `trick`, `basic`, `bit manipulation`, `bit`	AGAIN*
0873	Length of Longest Fibonacci Subsequence	Python , Java	O(n^2)	O(n)	Medium	hash table, `trick`, `DP`, `Fibonacci`, `set`, `amazon`, `apple`	AGAIN**
0957	Prison Cells After N Days	Python , Java	O(1)	O(1)	Medium	hash table, `trick`, `DP`, `mod`, `amazon`, `apple`	AGAIN (not start)
0966	Vowel Spellchecker	Python , Java	O(n)	O(w)	Medium	hash table, `trick`, `dict`, `set`, `amazon`	AGAIN (not start)
0974	Subarray Sums Divisible by K	Python , Java	O(n)	O(k)	Medium	hash table, LC 560, 525, 974, prefix, hashmap, `google`, `amazon`, `fb`, `apple`	AGAIN*************** (7)(MUST)
0992	Subarrays with K Different Integers	Python , Java	O(n)	O(k)	Hard	hash table, trick, hashmap, slide window, `amazon`, `google`, `apple`, `uber`	AGAIN**** (1)
1010	Pairs of Songs With Total Durations Divisible by 60	Python , Java	O(n)	O(1)	Medium	hash table, good basicm dict, array, `amazon`, `google`	AGAIN********* (4) (MUST)
1099	Two Sum Less Than K	Python , Java	O(nlogn)	O(1)	Medium	hash table, dict, sort, `amazon`, `array`, `two pointers`, `binary search`, `fb`	AGAIN* (1) (not start)
1121	Divide Array Into Increasing Sequences	Java	O(n)	O(1)	Hard	hash table, dict, `google`, `array`, `counting`	Again (not start)
1131	Rank Transform of an Array	Python , Java	O(nlogn)	O(n)	Easy	hash table, dict, array, `amazon`, `math`, `google`, `microsoft`	OK* (1)
1170	Compare Strings by Frequency of the Smallest Character	Java	O((m + n) l + nlogn)*	O(n)	Medium	hash table, hashmap, binary search, `google`, `amazon`	AGAIN*** (1)s
1257	Smallest Common Region	Java	O(n)	O(n)	Medium	hash table, hashmap, good trick, lowest common ancestor (LCA), `amazon`	AGAIN (not start)
1296	Divide Array in Sets of K Consecutive Numbers	Python , Java	O(nlogn)	O(n)	Medium	hash table, LC 846, dict, `google`	AGAIN (not start)
1726	Tuple with Same Product	Python , Java	O(n^2)	O(n^2)	Medium	hash table, hashmap, sort, 2 pointers, brute force, good basic, `google`	AGAIN**** (1)(MUST)
1794	Count Pairs of Equal Substrings With Minimum Difference	Java	O(m + n)	O(1)	Medium	hash table, first, last idx, hashmap, trick, `google`	AGAIN**** (1)(not start)
1923	Longest Common Subpath	Python, Java	O(m nlogn)*	O(n)	Hard	hash table, hash, bit, `amazon`, `array`, `binary search`, `rolling hash`	AGAIN (not start)
2506	Count Pairs Of Similar Strings	Java	O(n l)*	O(n)	Easy	hash table, hashmap, LC weekly	AGAIN (1)
2592	Maximize Greatness of an Array	Java	O(nlogn)	O(1)	Medium	hash table, Treemap, 2 pointers, LC weekly, `array`, `greedy`	AGAIN (1)
2615	Sum of Distances	Python , Java	O(n)	O(n)	Medium	hash table, good basic, left-right dist, prefix sum, hashmap, LC weekly	AGAIN************** (5)(MUST)
2766	Relocate Marbles	Java	O(n + m)	O(n)	Medium	hash table, hashset, hashmap LC weekly, good trick	AGAIN******(1)
2768	Number of Black Blocks	Java	O(n)	O(n)	Medium	hash table, hashmap, LC weekly	AGAIN(1) (not srart)
2870	Minimum Number of Operations to Make Array Empty	Java	O(n)	O(n)	Medium	hash table, LC 2244, hashmap, count, LC weekly	AGAIN (1)
2963	Count the Number of Good Partitions	Java	O(n)	O(n)	Hard	hash table, LC weekly	AGAIN (1) (not start)
3121	Count the Number of Special Characters II	Java	O(n)	O(1)	Medium	hash table, greedy, hashmap	AGAIN(1) (not srart)
4007	Minimum Initial Strength to Defeat All Monsters	Python, Java	O(n + m + nlog(sum))	O(n)	Medium	hash table, good trick, hashmap pair, LC weekly	AGAIN(1) (not srart)
4038	Count Integers Appearing in a Single Block	Python	O(n)	O(n)	Easy	hash table, hashmap, `span == cnt` trick, first/last idx, LC weekly	AGAIN(1)

Linked list

#	Title	Solution	Time	Space	Difficulty	Note	Status
0002	Add Two Numbers	Python, Java	O(n)	O(1)	Medium	linked list, check `# 445 Add Two Numbers II`, `basic`, `airbnb`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`	OK**** (6) (but again)
0021	Merge Two Sorted Lists	Python, Java	O(n)	O(1)	Easy	linked list, `uber`, `amazon`, `apple`, `fb`, `google`, `microsoft`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK******** (6) (but again)
0023	Merge k sorted lists	Python, Java	O(nlogk)	O(k)	Hard	linked list, check `#21 Merge Two Sorted Lists`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK**** (2) (but again !!!
0024	Swap Nodes in Pairs	Python, Java	O(n)	O(1)	Medium	linked list, `GOOD basic`, LC 100 like, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `bloomberg`, `top100liked`	AGAIN**************** (8) (MUST)
0025	Reverse Nodes in k-Group	Python, Java	O(n)	O(1)	Hard	linked list, good trick, reverse linkedlist, reverse K linkedlist, `amazon`, `google`, `fb`, `microsoft`, `apple`, `uber`, `neetcode150`, `top100liked`	AGAIN********** (4)
0061	Rotate List	Python, Java	O(n)	O(1)	Medium	linked list, `basic`, `amazon`, `apple`, `microsoft`, `linkedin`	AGAIN (2)
0082	Remove Duplicates from Sorted List II	Python, Java	O(n)	O(1)	Medium	linked list, good basic, check `# 083 Remove Duplicates from Sorted List`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN (3) *****
0083	Remove Duplicates from Sorted List	Python, Java	O(n)	O(1)	Easy	linked list, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK*
0092	Reverse Linked List II	Python, Java	O(n)	O(1)	Medium	linked list, LC 206, reverse k nodes, `good trick`, `fb`, `apple`, `google`, `amazon`, `microsoft`, `bloomberg`, `neetcode250`	AGAIN*************** (10) (MUST)
0138	Copy List with Random Pointer	Python, Java	O(n)	O(n)	Medium	linked list, trick, recursive, `hash table`, `uber`, `microsoft`, `amazon`, `fb`, `google`, `apple`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN******* (7)
0160	Intersection of Two Linked Lists	Python, Java	O(m + n)	O(1)	Easy	linked list, basic, hash table, 2 pointers, `airbnb`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `top100liked`	OK******* (7) (again!)
0203	Remove Linked List Elements	Python , Java	O(n)	O(1)	Easy	linked list, linked list basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN**** (3)
0206	Reverse Linked List	Python, Java	O(n)	O(1)	Easy	linked list, `good basic`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	OK*********** (9) (MUST again)
0234	Palindrome Linked List	Python, Java	O(n)	O(1)	Easy	linked list, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `top100liked`	OK (4)
0237	Delete Node in a Linked List	Python, Java	O(1)	O(1)	Easy	linked list, LintCode, `apple`, `google`, `amazon`, `fb`, `microsoft`	OK * (1) (but again)
0328	Odd Even Linked List	Python, Java	O(n)	O(1)	Medium	linked list, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	OK** (2)
0369	Plus One Linked List	Python, Java	O(n)	O(1)	Medium	linked list, 🔒, `basic`, `google`, `amazon`	AGAIN****** (3)
0430	Flatten a Multilevel Doubly Linked List	Python, Java	O(n)	O(n)	Medium	linked list, `good trick`, `doubly linked list`, `dfs`, iterative, stack, `fb`, `google`, `amazon`, `microsoft`, `uber`, `bloomberg`	AGAIN******** (6)
0445	Add Two Numbers II	Python, Java	O(m + n)	O(m + n)	Medium	linked list, `trick`, string, `good basic`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`	AGAIN*** (3)
0707	Design Linked List	Python, Java	get/addAtIndex/deleteAtIndex: O(n), addAtHead/addAtTail: O(1)	O(n)	Medium	linked list, linked list basic OP, `google`, `amazon`, `apple`, `microsoft`	AGAIN (1)
0708	Insert into a Cyclic Sorted List	Python, Java	O(n)	O(1)	Medium	linked list, `AGAIN`, `cyclic linked list`, `good trick`, `google`, `amazon`, `fb`, `microsoft`	AGAIN******** (4)
0725	Split Linked List in Parts	Python, Java	O(n + k)	O(1)	Medium	linked list, mod, split linked list, good trick, `amazon`, `google`, `apple`	AGAIN************ (6) (again)
0817	Linked List Components	Python, Java	O(m + n)	O(m)	Medium	linked list, set, array, `google`	AGAIN** (1)
1836	Remove Duplicates From an Unsorted Linked List	Java	O(n)	O(n)	Medium	linked list, hashset of seen values, dummy head, `good basic`, `microsoft`	AGAIN (not start)

Stack

#	Title	Solution	Time	Space	Difficulty	Note	Status
0020	Valid Parentheses	Python, Java	O(n)	O(n)	Easy	stack, `good basic`, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK** (6)
0032	Longest Valid Parentheses	Python, Java	O(n)	O(n)	Hard	stack, brute force, dp, deque, `amazon`, `fb`, `microsoft`, `google`, `apple`, `uber`, `top100liked`	AGAIN********** (3)
0071	Simplify Path	Python, Java	O(n)	O(n)	Medium	stack, `basic`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `neetcode250`	AGAIN******** (5)
0085	Maximal Rectangle	Python, Java	O(m n)*	O(n)	Hard	stack, top-100-like, brute force, dp, LC 84, `google`, `amazon`, `apple`, `fb`, `microsoft`, `uber`	AGAIN (not start)
0101	Symmetric Tree	Python, Java	O(n)	O(h)	Easy	stack, `good basic`, `bfs`, `dfs`, `linkedin`, `microsoft`, `amazon`, `fb`, `google`, `tree`, `apple`, `uber`, `bloomberg`, `top100liked`	AGAIN************* (7)
0150	Evaluate Reverse Polish Notation	Python, Java	O(n)	O(n)	Medium	stack, good trick, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `neetcode150`	AGAIN********* (5)
0155	Min Stack	Python, Java	O(1) per op	O(n)	Medium	stack, basic, data structure, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`	OK (but again)*********** (7)
0173	Binary Search Tree Iterator	Python, Java	ctor: O(h), next: O(1) amortized, hasNext: O(1)	O(h)	Medium	stack, `good basic`, `tree`, `microsoft`, `linkedin`, `google`, `amazon`, `fb`, `apple`, `uber`, `bloomberg`	OK***** (5)
0224	Basic Calculator	Python, Java	O(n)	O(n)	Hard	stack, `basic`, `trick`, LC 227, 772, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN******* (3)
0227	Basic Calculator II	Python, Java	O(n)	O(n)	Medium	stack, delay op, LC 224, 772, `good trick`, `airbnb`, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`	AGAIN************** (8) (MUST)
0232	Implement Queue using Stacks	Python, Java	O(1), amortized	O(n)	Easy	stack, stack-queue, EPI, LintCode, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`	AGAIN*** (3)(MUST)
0255	Verify Preorder Sequence in Binary Search Tree	Python, Java	O(n)	O(n)	Medium	stack, 🔒, `uber`	AGAIN (not start)
0321	Create Maximum Number	Java	O(k^2 (m + n))*	O(m + n)	Hard	stack, dp, greedy, mono-stack, `google`, `amazon`, `apple`	AGAIN (not start) (2)
0331	Verify Preorder Serialization of a Binary Tree	Python, Java	O(n)	O(1)	Medium	stack, slot counting (no stack needed), preorder serialization, `good trick`, `google`	AGAIN (not start)
0341	Flatten Nested List Iterator	Python, Java	O(n)	O(n)	Medium	stack, LC 284, 🔒 Iterator, generator, `good basic`, `amazon`, `fb***`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN********* (6)
0385	Mini Parser	Python, Java	O(n)	O(n)	Medium	stack, parse nested list, recursion, `good basic`, `google`	AGAIN
0394	Decode String	Python, Java	O(n)	O(n)	Medium	stack, good basic!!!, pre num string, LC 224, 227, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`, `top100liked`	AGAIN******************* (10) (MUST)
0439	Ternary Expression Parser	Python, Java	O(n)	O(n)	Medium	stack, 🔒	AGAIN (not start)
0456	132 Pattern	Python, Java	O(n)	O(n)	Medium	stack, binary search, `google`, `amazon`, `microsoft`	AGAIN (not start)
0496	Next Greater Element I	Python, Java	O(n)	O(n)	Easy	stack, good basic, mono stack, LC 739, LC 503, LC 406, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	OK*************** (6) (but again)
0503	Next Greater Element II	Python, Java	O(n)	O(n)	Medium	stack, good basic, LC 739, LC 503, LC 406, next_big_val_idx, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN************* (7)
0591	Tag Validator	Java	O(n)	O(n)	Hard	stack, parse tags + CDATA, `complex`, string, `google`, `amazon`, `microsoft`, `uber`	AGAIN (not start)
0636	Exclusive Time of Functions	Python, Java	O(n)	O(n)	Medium	stack, `trick`, `AGAIN`, `uber`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `linkedin`	AGAIN********** (4)
0682	Baseball Game	Python, Java	O(n)	O(n)	Easy	stack, good basic, `amazon`, `google`, `neetcode250`	OK* (3)
0735	Asteroid Collision	Python, Java	O(n)	O(n)	Medium	stack, good basic, `microsoft`, `goldman sachs`, `fb`, `amazon`, `google`, `uber`, `neetcode250`	AGAIN************** (5)
0739	Daily Temperatures	Python, Java	O(n)	O(n)	Medium	stack, LC 739, LC 503, LC 406, LC 496, LC 42, Monotonic stack, good trick, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN******************* (12) (MUST)
0772	Basic Calculator III	Java	O(n)	O(n)	Hard	stack, check LC 224, 227, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN (not start)
0853	Car Fleet	Python, Java	O(nlogn)	O(n)	Medium	stack, good basic, `google`, `amazon`, `neetcode150`	AGAIN********* (5)
0856	Score of Parentheses	Python, Java	O(n)	O(n)	Medium	stack, stack of scores, or count depth on each `()`, `good trick`, `google`, `amazon`, `fb`	AGAIN (not start)
0872	Leaf-Similar Trees	Python, Java	O(n)	O(h)	Easy	stack, top down, bottom up dfs, good basic, `tree`, `binary tree`, `google`, `amazon`, `fb`	AGAIN***** (MUST)
0895	Maximum Frequency Stack	Python, Java	push: O(1), pop: O(1)	O(n)	Hard	stack, good basic, heap, design, `amazon`, `apple`, `linkedin`, `microsoft`, `twitter`, `google`, `fb`, `uber`, `neetcode250`	AGAIN********** (1) (not start)
0901	Online Stock Span	Python, Java	O(n)	O(n)	Medium	stack, mono stack, good basic, `google`, `amazon`, `fb`, `microsoft`, `neetcode250`	AGAIN***** (2)
0946	Validate Stack Sequences	Python, Java	O(n)	O(n)	Medium	stack, simulate push/pop with one stack, `good basic`, `google`, `amazon`, `fb`, `microsoft`, `linkedin`	AGAIN
1028	Recover a Tree From Preorder Traversal	Java	O(n)	O(n)	Hard	stack, brute force, `google`, `string`, `tree`, `dfs`, `amazon`, `linkedin`	AGAIN (not start)
1047	Remove All Adjacent Duplicates in String	Python, Java	O(n)	O(n)	Easy	stack, good basic, LC 1209, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`	AGAIN************ (3) (MUST)
1081	Smallest Subsequence of Distinct Characters	Java	O(n)	O(n)	Medium	stack, LC 316, `google`, `amazon`	AGAIN (1)
1209	Remove All Adjacent Duplicates in String II	Python, Java	O(n)	O(n)	Medium	stack, LC 1047, good basic, two pointers, greedy, `fb`, amamzon, `apple`, spotify, `google`, `amazon`, `microsoft`, `bloomberg`	AGAIN***************** (4) (MUST)
1544	Make The String Great	Java	O(n)	O(n)	Easy	stack, LC 1047, remove adjacent opposite-case pairs, `basic`, `google`	AGAIN(1)
1703	Minimum Adjacent Swaps for K Consecutive Ones	Python, Java	O(n)	O(n)	Hard	stack, heap, sliding window, `amazon`, `array`, `greedy`, `google`, `microsoft`	AGAIN (not start)
1896	Minimum Cost to Change the Final Value of Expression	Python, Java	O(n)	O(n)	Hard	stack, complex, dp, dp+stack, dfs, `amazon`, `google`	AGAIN (not start)
2104	Sum of Subarray Ranges	Python, Java	O(n)	O(n)	Medium	stack, LC 907, good basic, monotonic stack, brute force, dp, `amazon`	AGAIN************ (5)
2289	Steps to Make Array Non-decreasing	Python, Java	O(n)	O(n)	Medium	stack, mono stack, mono stack + dp, good trick	AGAIN************ (2) (MUST)
4045	Count Robot Groups	Python	O(n)	O(1)	Medium	stack, car fleet (LC 853), right -> left scan, merge keeps the rightmost robot’s state, t=0 touch chains via the neighbour, LC weekly	AGAIN(1)

Tree

#	Title	Solution	Time	Space	Difficulty	Note	Status
0094	Binary Tree Inorder Traversal	Python, Java	O(n)	O(h)	Medium	tree, iteration, recursion, `good basic`, `Morris Traversal`, `microsoft`, `fb`, `google`, `amazon`, `bloomberg`, `neetcode250`, `top100liked`	AGAIN********* (4) (MUST)
0124	Binary Tree Maximum Path Sum	Python, Java	O(n)	O(h)	Hard	tree, `google`, `amazon`, `fb`, `microsoft`, `twitter`, `apple`, `uber`, `bloomberg`, `blind75`, `top100liked`	AGAIN*********** (6) (MUST)
0144	Binary Tree Preorder Traversal	Python, Java	O(n)	O(h)	Medium	tree, `Morris Traversal`, `google`, `amazon`, `apple`, `uber`, `neetcode250`	OK
0145	Binary Tree Postorder Traversal	Java	O(n)	O(h)	Medium	tree, `Morris Traversal`, `google`, `amazon`, `fb`, `apple`, `neetcode250`	OK
0208	Implement Trie (Prefix Tree)	Python, Java	insert/search/startsWith: O(l)	O(t)	Medium	tree, dict tree, LC 211, trie, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	AGAIN************** (7) (MUST)
0211	Design Add and Search Words Data Structure	Python, Java	add: O(l), search: O(n l)* worst	O(t)	Medium	tree, `Trie`, recursive, node, hashMap, do `# 208 first`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `blind75`	AGAIN*********** (9) (MUST)
0226	Invert Binary Tree	Python, Java	O(n)	O(h)	Easy	tree, good basic, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	OK******* (4) (but again)
0250	Count Univalue Subtrees	Python, Java	O(n)	O(h)	Medium	tree, LC 572, `google`, `amazon`, `fb`, `bloomberg`	not start
0297	Serialize and Deserialize Binary Tree	Python, Java	O(n)	O(n)	Hard	tree, LC 449, BFS, DFS, Binary Tree, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`	again******* (4)
0307	Range Sum Query - Mutable	Python, Java	ctor: O(n), update: O(logn), query: O(logn)	O(n)	Medium	tree, LintCode, DFS, Segment Tree, BIT, check `#303 Range Sum Query - Immutable`, `google`, `array`, `divide and conquer`, `design`, `amazon`, `fb`	AGAIN* (2)(not start)
0427	Construct Quad Tree	Java	O(n^2 logn)*	O(logn)	Medium	tree, Quadtrees, `google`, `amazon`, `apple`, `microsoft`, `uber`, `neetcode250`	again (not start)
0508	Most Frequent Subtree Sum	Python, Java	O(n)	O(n)	Medium	tree, dfs, bfs, good basic, `amazon`, `google`, `apple`	OK*********** (4) (but again MUST)
0536	Construct Binary Tree from String	Python, Java	O(n)	O(h)	Medium	tree, 🔒, recursive, str->tree, check LC 606, `amazon`, `google`, `fb`	AGAIN******** (6)
0538	Convert BST to Greater Tree	Python, Java	O(n)	O(h)	Medium	tree, good basic, dfs, BST, cum sum, `amazon`, `fb`, `microsoft`	OK************** (6)(MUST)
0543	Diameter of Binary Tree	Python, Java	O(n)	O(h)	Easy	tree, dfs, `trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN*********** (7)(MUST)
0545	Boundary of Binary Tree	Python, Java	O(n)	O(h)	Medium	tree, recursive, dfs, tree boundary, 🔒, `good trick`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN********* (6)
0548	Split Array with Equal Sum	Python, Java	O(n^2)	O(n)	Medium	tree, 🔒, `good trick`, `array`, `hash table`, `prefix sum`, `fb`	AGAIN*** (2)
0563	Binary Tree Tilt	Python, Java	O(n)	O(h)	Easy	tree, post-order dfs, subtree sum, `good basic`	AGAIN
0572	Subtree of Another Tree	Python, Java	O(m n)*	O(h)	Easy	tree, LC 100, recursive call recursion func, good basic, dfs, bfs, `amazon`, `fb`, `google`, `microsoft`, `bloomberg`, `blind75`	OK************* (10) (but again)
0606	Construct String from Binary Tree	Python, Java	O(n)	O(h)	Easy	tree, good basic, tree->str, dfs, LC 536, `amazon`, `fb`	OK************ (8) (again!)
0617	Merge Two Binary Trees	Python, Java	O(n)	O(h)	Easy	tree, dfs, bfs, `good basic`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	OK************* (7) (but again)
0623	Add One Row to Tree	Python, Java	O(n)	O(h)	Medium	tree, `good basic`, `dfs`, `bfs`, re-connect tree, `microsoft`	AGAIN***************** (5)(MUST)
0637	Average of Levels in Binary Tree	Python, Java	O(n)	O(h)	Easy	tree, `bfs`, `dfs`, `good basic`, `fb`, `google`, `amazon`, `microsoft`	OK*** (4)
0652	Find Duplicate Subtrees	Python, Java	O(n)	O(n)	Medium	tree, good basic, serialization, path, bfs, dfs, Hashmap, `amazon`, `google`, `fb`, `microsoft`, `bloomberg`	AGAIN************** (9)(MUST)
0653	Two Sum IV - Input is a BST	Python, Java	O(n)	O(h)	Easy	tree, Two Pointers, `2 sum`, `bfs`, `dfs`, `amazon`, `fb`, `google`, `microsoft`, `uber`	OK******* (4)
0654	Maximum Binary Tree	Python, Java	O(n) ~ O(n^2)	O(n)	Medium	tree, LintCode, Descending Stack, `good basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN* (2)
0655	Print Binary Tree	Python, Java	O(n)	O(n)	Medium	tree, matrix, dfs, bfs, good basic, `google`, `amazon`, `fb`, `uber`, `linkedin`	AGAIN****** (3)
0662	Maximum Width of Binary Tree	Python, Java	O(n)	O(n)	Medium	tree, tree width, bfs, dfs, `trick`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN************* (5)(MUST)
0663	Equal Tree Partition	Python, Java	O(n)	O(n)	Medium	tree, `# LC 508`, AGAIN, 🔒, Hash, dfs, `trick`, `good trick`, `amazon`, `fb`	OK******** (8)
0677	Map Sum Pairs	Python, Java	insert: O(l), sum: O(p + t)	O(t)	Medium	tree, Trie, `trick`, `hard`, `google`	AGAIN* (2) (not start)
0683	K Empty Slots	Python, Java	O(n)	O(n)	Hard	tree, BST, bucket, `google`, `array`, `binary indexed tree`, `segment tree`, `amazon`	not start
0684	Redundant Connection	Python, Java	O(n)	O(n)	Medium	tree, dfs, graph, Union Find, `basic`, `bfs`, `google`, `amazon`, `neetcode150`	AGAIN****** (3) (not start)
0687	Longest Univalue Path	Python, Java	O(n)	O(h)	Medium	tree, dfs, good basic, path, `google`, `amazon`	AGAIN********* (5)
0701	Insert into a Binary Search Tree	Python, Java, Java-followup	O(h)	O(h)	Medium	tree, good basic, BST, BFS, DFS, `google`, `amazon`, `fb`, `microsoft`, `linkedin`, `neetcode250`	OK***** (3)
0814	Binary Tree Pruning	Python, Java	O(n)	O(h)	Medium	tree, prune, good basic, DFS, `basic`, LC 1325, `google`, `amazon`, `fb`, `apple`	AGAIN*********** (3)(MUST)
0834	Sum of Distances in Tree	Java	O(n)	O(n)	Hard	tree, DP, re-rooting pattern, `google`, `amazon`, `apple`	AGAIN****** (1) (not start)
0863	All Nodes Distance K in Binary Tree	Python, Java	O(n)	O(n)	Medium	tree, LC 752, tree -> graph, radiate outward, DFS + BFS, good basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN**************** (5)(MUST)
0865	Smallest Subtree with all the Deepest Nodes	Python, Java	O(n)	O(h)	Medium	tree, LC 1123, LCA, dfs, `basic`, `amazon`, `fb`	AGAIN***************** (6)(MUST)
0889	Construct Binary Tree from Preorder and Postorder Traversal	Python, Java	O(n)	O(h)	Medium	tree, `DFS`, `stack`, `trick`, recursive, `google`, `amazon`, `fb`, `uber`	AGAIN** (2) (not start*)
0897	Increasing Order Search Tree	Python, Java	O(n)	O(h)	Easy	tree, `DFS`, `good basic`, `inorder`, `google`, `amazon`, `fb`, `apple`	AGAIN** (2)
0919	Complete Binary Tree Inserter	Python, Java	ctor: O(n) insert: O(1) get_root: O(1)	O(n)	Medium	tree, `bst`, `google`, `amazon`, `fb`, `microsoft`	AGAIN** (2)
0938	Range Sum of BST	Python, Java	O(n)	O(h)	Easy	tree, DFS, check `# 108 Convert Sorted Array to Binary Search Tree`, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK* (2)
0951	Flip Equivalent Binary Trees	Python, Java	O(n)	O(h)	Medium	tree, recursion, DFS, `google`, `amazon`, `fb`	AGAIN***s (3)
0958	Check Completeness of a Binary Tree	Python, Java	O(n)	O(w)	Medium	tree, `BFS`, `DFS`, `basic`, `google`, `amazon`, `fb`, `microsoft`	AGAIN** (2)
0965	Univalued Binary Tree	Python, Java	O(n)	O(h)	Easy	tree, `DFS`, `BFS`, `good basic`, `google`	AGAIN** (2)
0971	Flip Binary Tree To Match Preorder Traversal	Python, Java	O(n)	O(h)	Medium	tree, DFS, `trick`	AGAIN** (2) (not start)
0979	Distribute Coins in Binary Tree	Python, Java	O(n)	O(h)	Medium	tree, DFS, `trick`, `google`, `amazon`, `fb`, `microsoft`	AGAIN************ (3) (MUSTS)
1032	Stream of Characters	Java	ctor: O(t), query: O(l)	O(t)	Hard	tree, trie, node, `google`, `amazon`, `fb`, `microsoft`	AGAIN****** (1)
1157	Online Majority Element In Subarray	Java	ctor: O(n), query: O(klogn)	O(n)	Hard	tree, `google`, `array`, `binary search`, `design`	AGAIN (not start)
1325	Delete Leaves With a Given Value	Java, Python	O(n)	O(h)	Medium	tree, dfs, post-order, LC 450, 814, `google`, `amazon`, `neetcode250`	AGAIN********** (4)(MUST)
1339	Maximum Product of Splitted Binary Tree	Python, Java	O(n)	O(h)	Medium	tree, dfs, `amazon`	AGAIN*** (1) (not start)
1372	Longest ZigZag Path in a Binary Tree	Python, Java	O(n)	O(h)	Medium	tree, dfs, bfs, post order, good trick, `amazon`	AGAIN*** (1) (not start)
1448	Count Good Nodes in Binary Tree	Python, Java	O(n)	O(h)	Medium	tree, max in path, dfs, bfs, good trick, needcode, `google`, `amazon`, `microsoft`, `neetcode150`	AGAIN************* (3) (MUST)
1522	Diameter of N-Ary Tree	Java	O(n)	O(h)	Medium	tree, LC 543, `fb`, `microsoft`	AGAIN (not start)
1666	Change the Root of a Binary Tree	Java	O(h)	O(h)	Medium	tree, LC 1448, good trick, `google`	AGAIN (1) (not start)
1740	Find Distance in a Binary Tree	Python, Java	O(n)	O(h)	Medium	tree, LCA, node dist, DFS, good basic, `google`, `amazon`, `apple`	AGAIN*************** (5)(MUST)
2331	Evaluate Boolean Binary Tree	Java	O(n)	O(h)	Easy	tree, DFS, good basic	OK (1)****
2415	Reverse Odd Levels of Binary Tree	Java	O(n)	O(n)	Medium	tree, LC 226, dfs, bfs	AGAIN (not start)
2509	Cycle Length Queries in a Tree	Java	O(q logn)*	O(1)	Hard	tree, LC weekly	AGAIN (not start)
2641	Cousins in Binary Tree II	Java	O(n)	O(n)	Medium	tree, LC weekly, LC 993	AGAIN (1)
2707	Extra Characters in a String	Java	O(n^2)	O(n + t)	Medium	tree, dp, Trie, `neetcode250`	AGAIN (not start)
3093	Longest Common Suffix Queries	Java	O(t + q l)*	O(t)	Hard	tree, Trie	AGAIN (not start)

Heap

#	Title	Solution	Time	Space	Difficulty	Note	Status
0264	Ugly Number II	Python, Java	O(n)	O(n)	Medium	heap, good trick, LC 263, LC 313, LintCode, DP, `microsoft`, `google`, `amazon`, `apple`	AGAIN*********** (4) (MUST)
0295	Find Median from Data Stream	Python, Java	addNum: O(logn), findMedian: O(1)	O(n)	Hard	heap, priority queue, trick, stream, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`, `netflix`	AGAIN****** (6)
0313	Super Ugly Number	Python, Java	O(n k)*	O(n + k)	Medium	heap, BST, `array`, `math`, `dp`, `google`, `amazon`, `fb`, `apple`	AGAIN (not start*)
0373	Find K Pairs with Smallest Sums	Python, Java	O(k log(min(n, m, k)))*	O(min(n, m, k))	Medium	heap, `google`, good basic, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN******* (1)
0378	Kth Smallest Element in a Sorted Matrix	Python, Java	O(klogn)	O(k)	Medium	heap, binary search, matrix, LintCode, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN** (1)
0502	IPO	Java	O(nlogn)	O(n)	Hard	heap, PQ, `amazon`, `uber`, `neetcode250`	AGAIN (not start)
0506	Relative Ranks	Java	O(nlogn)	O(n)	Easy	heap, PQ, sort, hashmap, `google`	AGAIN (not start)
0703	Kth Largest Element in a Stream	Python, Java	ctor: O(nlogk), add: O(logk)	O(k)	Easy	heap, priority queue, `amazon`, `google`, `fb`, `apple`, `microsoft`, `neetcode150`	AGAIN******** (5)
0846	Hand of Straights	Python, Java	O(nlogn)	O(n)	Medium	heap, LC 1296, good basic, PQ, Treemap, hashmap, `google`, `array`, `greedy`, `apple`, `neetcode150`	OK******** (3)
0855	Exam Room	Python, Java	seat: O(logn) leave: O(logn)	O(n)	Medium	heap, treeSet, BST, Hash, `trick`, LC 849, `google`, `fb`, `uber`	AGAIN* (3) (not start)
1046	Last Stone Weight	Python, Java	O(nlogn)	O(n)	Easy	heap, Priority Queue, `google`, `amazon`, `neetcode150`	OK
1054	Distant Barcodes	Java	O(nlogn)	O(n)	Medium	heap, PQ, LC 767, `amazon`	Again (1)
1130	Minimum Cost Tree From Leaf Values	Python, Java	O(n)	O(n)	Medium	heap, LC 1167, monotonic stack (O(n)) or interval dp (O(n^3)), greedy, `array`, `amazon`	not start
1167	Minimum Cost to Connect Sticks	Python, Java	O(nlogn)	O(n)	Medium	heap, LC 1130, good basic, `amazon`, `google`	AGAIN***** (3)
1353	Maximum Number of Events That Can Be Attended	Python, Java	O(nlogn)	O(n)	Medium	heap, LC 252, 253, good trick, meeting room, PRIORITY QUEUE, `fb`, `twitter`, `amazon`, `google`, `apple`, `microsoft`	AGAIN********* (4) MUST
1383	Maximum Performance of a Team	Java	O(nlogn)	O(n)	Hard	heap, PQ, `amazon`	AGAIN***** (1)
1405	Longest Happy String	Python, Java	O(n)	O(1)	Medium	heap, PQ, most_freq, LC 767, `amazon`, `microsoft`, `neetcode250`	AGAIN************* (2) (MUST)
1438	Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit	Java	O(n)	O(n)	Medium	heap, PQ, treemap, dequeue, `google`, `amazon`, `uber`	AGAIN (not start)
1481	Least Number of Unique Integers after K Removals	Python, Java	O(nlogn)	O(n)	Medium	heap, good trick, greedy, Counter, dict, `amazon`, `array`, `fb`	AGAIN******** (3)
1642	Furthest Building You Can Reach	Python	O(nlogn)	O(n)	Medium	heap, min-heap keeps the `ladders` biggest climbs, pay bricks for the smallest, `greedy`, `good trick`, `google`, `amazon`, `microsoft`	AGAIN(1)
1647	Minimum Deletions to Make Character Frequencies Unique	Java	O(nlogn)	O(n)	Medium	heap, greedy, PQ, good trick, `hash table`, `string`, `amazon`, `apple`, `microsoft`	AGAIN***********(2)
1675	Minimize Deviation in Array	Java	O(nlogn logM)*	O(n)	Hard	heap, PQ, `amazon`	AGAIN (not start)
1834	Single-Threaded CPU	Java	O(nlogn)	O(n)	Medium	heap, good trick, pq, `google`, `fb`, `neetcode250`	AGAIN***** (1)
1882	Process Tasks Using Servers	Python	O((n + m) logn)*	O(n)	Medium	heap, two heaps (free by weight / busy by free-time), wait branch clocks from free_at not j, LC 1834, `google`, `amazon`	AGAIN(1)
2406	Divide Intervals Into Minimum Number of Groups	Python, Java	O(nlogn)	O(n)	Medium	heap, LC 253, PQ, sort, scan line, good basic	AGAIN********** (2) (MUST)
2542	Maximum Subsequence Score	Java	O(nlogn)	O(n)	Medium	heap, pq with pair, good trick, sort	AGAIN (1)
2593	Find Score of an Array After Marking All Elements	Java	O(nlogn)	O(n)	Medium	heap, good trick, pq, sort, slide window, LC weekly	AGAIN***** (1)
3092	Most Frequent IDs	Python, Java	O(nlogn)	O(n)	Medium	heap, PQ, lazy delete, hashmap, LC weekly	AGAIN********** (MUST) (1)

Bit Manipulation

#	Title	Solution	Time	Space	Difficulty	Note	Status
0136	Single Number	Python, Java	O(n)	O(1)	Easy	bit manipulation, `airbnb`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	OK
0137	Single Number II	Python, Java	O(n)	O(1)	Medium	bit manipulation, LC 136, count bits mod 3 / ones-twos state machine, `good trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK
0190	Reverse Bits	Python, Java	O(1)	O(1)	Easy	bit manipulation, bit, `apple`, `google`, `amazon`, `fb`, `microsoft`, `blind75`	AGAIN*** (2)
0191	Number of 1 Bits	Python, Java	O(1)	O(1)	Easy	bit manipulation, `apple`, `google`, `amazon`, `fb`, `microsoft`, `blind75`	OK*
0201	Bitwise AND of Numbers Range	Python, Java	O(1)	O(1)	Medium	bit manipulation, common binary prefix, shift right until m == n, `trick`, `amazon`, `fb`, `neetcode250`	AGAIN (not start)
0231	Power of Two	Python, Java	O(1)	O(1)	Easy	bit manipulation, good basic, `amazon`, `google`, `apple`, `microsoft`	OK*** (3)
0260	Single Number III	Python, Java	O(n)	O(1)	Medium	bit manipulation, `xor`, `^=`, `^`, `google`, `amazon`, `fb`, `apple`	AGAIN*
0268	Missing Number	Python, Java	O(n)	O(1)	Easy	bit manipulation, `xor`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `bloomberg`, `blind75`	OK* (2)
0318	Maximum Product of Word Lengths	Python, Java	O(n^2 + n l)*	O(n)	Medium	bit manipulation, Counting Sort, Pruning, `google`	AGAIN (not start)
0342	Power of Four	Python, Java	O(1)	O(1)	Easy	bit manipulation, `power of num`	OK*
0371	Sum of Two Integers	Python, Java	O(1)	O(1)	Medium	bit manipulation, `good basic`, `fb`, `amazon`, `apple`, `microsoft`, `uber`, `blind75`	AGAIN********* (5) (bit op not start)
0389	Find the Difference	Python, Java	O(n)	O(1)	Easy	bit manipulation, `amazon`, `google`, `fb`	OK (2)
0393	UTF-8 Validation	Python, Java	O(n)	O(1)	Medium	bit manipulation, `utf-8 encoding`, `google`, `fb`, `amazon`, `apple`	AGAIN**** (not start*) (5)
0401	Binary Watch	Python, Java	O(1)	O(1)	Easy	bit manipulation, enumerate the 12 * 60 times or use bit count, brute force, `basic`, `google`, `apple`	OK*
0421	Maximum XOR of Two Numbers in an Array	Python, Java	O(n)	O(n)	Medium	bit manipulation, Trie of bits or prefix hashset, greedy from the MSB, `good trick`, `google`, `amazon`, `microsoft`	AGAIN (not start)
0461	Hamming Distance	Python, Java	O(1)	O(1)	Easy	bit manipulation, `fb`, `google`, `amazon`	OK* (2)
0462	Minimum Moves to Equal Array Elements II	Python, Java	O(n) on average	O(1)	Medium	bit manipulation, median minimizes the sum of absolute diffs, quick select, sort, `math`, `array`, `microsoft`	AGAIN*
0477	Total Hamming Distance	Python, Java	O(n)	O(1)	Medium	bit manipulation, `fb`, `amazon`	AGAIN****** (not start*) (4)
0645	Set Mismatch	Python, Java	O(n)	O(1)	Easy	bit manipulation, `amazon`, `fb`	OK* (3)
0693	Binary Number with Alternating Bits	Python, Java	O(1)	O(1)	Easy	bit manipulation, `trick`	AGAIN*
0762	Prime Number of Set Bits in Binary Representation	Python, Java	O(1)	O(1)	Easy	bit manipulation, `basic`, `prime number`, `amazon`	OK* (4)
0868	Binary Gap	Python, Java	O(1)	O(1)	Easy	bit manipulation, `trick`, `linear scan`	AGAIN*
0898	Bitwise ORs of Subarrays	Python, Java	O(n logM)*	O(logM)	Medium	bit manipulation, set of distinct ORs per index (at most logM), `good trick`, `amazon`	AGAIN (not start)
1573	Number of Ways to Split a String	Python, Java	O(n)	O(1)	Medium	bit manipulation, `amazon`, binary, `math`, `string`	AGAIN** (not start)
1915	Number of Wonderful Substrings	Python, Java	O(n)	O(1)	Medium	bit manipulation, bit mask, bit, prefix sum, dp, `amazon`, `google`	AGAIN*** (2) (not start)
2683	Neighboring Bitwise XOR	Java	O(n)	O(1)	Medium	bit manipulation, bit op, simulation LC weekly 345	AGAIN*** (1)
2871	Split Array Into Maximum Number of Subarrays	Java	O(n)	O(1)	Medium	bit manipulation, bit op, LC weekly	AGAIN*** (1)
3688	Bitwise OR of Even Numbers in an Array	Java	O(n)	O(1)	Easy	bit manipulation, bit mask	OK

String

#	Title	Solution	Time	Space	Difficulty	Note	Status
0005	Longest Palindromic Substring	Python, Java	O(n^2)	O(1)	Medium	string, LC 647, good trick, 2 pointer, recursive, `Manacher's Algorithm`, LC 100 like, `DP`, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `bloomberg`, `blind75`, `top100liked`	AGAIN******************* (8)(MUST)
0006	ZigZag Conversion	Python, Java	O(n)	O(n)	Medium	string, simulate the rows, `basic`, `trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN (not start)
0008	String to Integer (atoi)	Python, Java	O(n)	O(1)	Medium	string, string op, `regular expression`, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`	AGAIN***** (5)
0014	Longest Common Prefix	Python, Java	O(n k)*	O(1)	Easy	string, `good basic`, LCP, prefix, binary search, scan, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`	AGAIN !!! (5)
0028	Implement strStr()	Python, Java	O(n + k)	O(k)	Easy	string, `KMP Algorithm`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`	OK (3)
0028	Find the Index of the First Occurrence in a String	Java	O(n + k)	O(k)	Easy	string, duplicate of LC 28, `KMP Algorithm`, `Rabin-Karp Algorithm`, two pointers, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`	OK (3)
0038	Count and Say	Python, Java	O(n 2^n)*	O(2^n)	Medium	string, `recursion`, `iteration`, basic, `fb`, `google`, `amazon`, `apple`, `microsoft`	AGAIN*********** (5)
0043	Multiply Strings	Python, Java	O(m n)*	O(m + n)	Medium	string, `twitter`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN*** (3)
0058	Length of Last Word	Python, Java	O(n)	O(1)	Easy	string, scan from the end, `basic`, `google`, `amazon`, `fb`, `microsoft`	OK
0067	Add Binary	Python, Java	O(n)	O(1)	Easy	string, bit op, `good basic`, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `neetcode250`	OK***** (7) (but again)
0076	Minimum Window Substring	Python, Java	O(m + n)	O(k)	Hard	string, slide window, good pattern, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN*********** (3)
0125	Valid Palindrome	Python, Java	O(n)	O(1)	Easy	string, LC 680, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`, `blind75`	OK
0151	Reverse Words in a String	Python, Java	O(n)	O(1)	Medium	string, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`	OK (2)
0161	One Edit Distance	Python, Java	O(m + n)	O(1)	Medium	string, 🔒, DP, 2 pointers, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN ************ (6)(MUST)
0165	Compare Version Numbers	Python, Java	O(n)	O(1)	Medium	string, good basic, `amazon`, `apple`, `google`, `microsoft`	OK** (5)
0186	Reverse Words in a String II	Python, Java	O(n)	O(1)	Medium	string, LC 151, LC 557, 🔒, `microsoft`, `uber`, `amazon`, `fb`	AGAIN* (3)
0242	Valid Anagram	Python, Java	O(n)	O(1)	Easy	string, LintCode, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`	OK
0271	Encode and Decode Strings	Python, Java	O(n)	O(1)	Medium	string, decode-encode, string op, check `# 394 Decode String`, 🔒, `google`, `fb`, `apple`, `microsoft`, `uber`, `blind75`	AGAIN******* (4)
0306	Addictive Number	Python, Java	O(n^3)	O(n)	Medium	string, backtracking over the first two numbers, big-int add, `dfs`, LC 842, `google`	AGAIN (not start*)
0340	Longest Substring with At Most K Distinct Characters	Python, Java	O(n)	O(k)	Hard	string, sliding window, `google`, `amazon`, `fb`, `microsoft`, `uber`, `bloomberg`	not start
0383	Ransom Note	Python, Java	O(n)	O(1)	Easy	string, EPI, `apple`, `google`, `amazon`, `fb`, `microsoft`	OK*
0405	Convert a Number to Hexadecimal	Python, Java	O(n)	O(1)	Easy	string, `basics` `decimal -> Hexadecimal`, `google`, `amazon`, `fb`	AGAIN
0408	Valid Word Abbreviation	Python, Java	O(n)	O(1)	Easy	string, 🔒, `google`, `fb`	AGAIN (not start)
0415	Add Strings	Python, Java	O(n)	O(1)	Easy	string, `good basic`, `add xxx to sum`, `airbnb`, `google`, `fb`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`	OK****** (4)
0434	Number of Segments in a String	Python, Java	O(n)	O(1)	Easy	string, count word starts, split, `basic`, `apple`	OK
0443	String Compression	Python, Java	O(n)	O(1)	Easy	string, shoptify, `basics`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN**
0459	Repeated Substring Pattern	Python, Java	O(n)	O(n)	Easy	string, good basic, `KMP Algorithm`, `amazon`, `google`, `fb`, `microsoft`	OK*** (6)
0468	Validate IP Address	Python, Java	O(1)	O(1)	Medium	string, `ip basic`, `twitter`, `fb`, `amazon`, `google`, `microsoft`	AGAIN****** (5)
0482	License Key Formatting	Python, Java	O(n)	O(1)	Easy	string, basic, `google`, `amazon`	OK** (4) (again)
0520	Detect Capital	Python, Java	O(l)	O(1)	Easy	string, three valid cases (all upper / all lower / leading capital), `basic`, `google`, `amazon`	OK
0521	Longest Uncommon Subsequence I	Python, Java	O(min(a, b))	O(1)	Easy	string, if the two strings differ the answer is max(len), `trick`, `google`	OK*
0522	Longest Uncommon Subsequence II	Python, Java	O(l n^2)*	O(1)	Medium	string, sort, compare all pairs, LC 521, `google`, `apple`	AGAIN (not start)
0524	Longest Word in Dictionary through Deleting	Python, Java	O(d l + d * logd)*	O(1)	Medium	string, good basic, sort, 2 pointers, subsequence check, `google`	AGAIN*********** (2)
0539	Minimum Time Difference	Python, Java	O(nlogn)	O(n)	Medium	string, `basic`, `map & zip trick`, `google`, `apple`	AGAIN**
0541	Reverse String II	Python, Java	O(n)	O(1)	Easy	string, reverse every 2k block, `basic`, `google`, `amazon`, `apple`, `microsoft`	AGAIN**** (1)
0551	Student Attendance Record I	Python, Java	O(n)	O(1)	Easy	string, count `A` and 3 consecutive `L`, `basic`, `google`	OK**
0556	Next Greater Element III	Python, Java	O(n)	O(n)	Medium	string, LC 31 next permutation applied to digits, `good trick`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
0557	Reverse Words in a String III	Python, Java	O(n)	O(1)	Easy	string, split, reverse each word, `basic`, `google`, `amazon`, `apple`, `microsoft`	OK
0616	Add Bold Tag in String	Python, Java	O(n d * l)*	O(n)	Medium	string, LC 758, 🔒, `google`, `fb`	AGAIN (not start)
0647	Palindromic Substrings	Python, Java	O(n^2)	O(1)	Medium	string, LC 005, greedy, 2D DP, expand from center, 2 pointers, `good basic`, `Manacher's Algorithm`, `linkedin`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `blind75`	OK************** (10) (MUST)
0648	Replace Words	Python, Java	O(n)	O(t)	Medium	string, Trie, hashset, `good basic`, `amazon`, `fb`, `uber`	AGAIN (2)*******
0657	Judge Route Circle	Python, Java	O(n)	O(1)	Easy	string, count moves per direction, LC 1041, `basic`, `google`, `amazon`	OK
0678	Valid Parenthesis String	Python, Java	O(n)	O(1)	Medium	string, greedy, dp, stack, `good trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN********** (3) (MUST)
0680	Valid Palindrome II	Python, Java	O(n)	O(1)	Easy	string, LC 125, two pointers, `good basic`, Palindrome, `fb`, `google`, `amazon`, `apple`, `microsoft`, `neetcode250`	AGAIN************* (4) (MUST)
0681	Next Closest Time	Python, Java	O(1)	O(1)	Medium	string, `subset of set`, `<=`, `strptime`, `google`, `fb`, `amazon`, `uber`	OK*** (5)
0686	Repeated String Match	Python, Java	O(n + m)	O(1)	Medium	string, brute force, math, `Rabin-Karp Algorithm`, `google`, `amazon`, `fb`	AGAIN**** (3)
0696	Count Binary Substrings	Python, Java	O(n)	O(1)	Easy	string, good trick, linear scan, group sub-string, `amazon`, `google`	AGAIN******* (3) (MUST)
0720	Longest Word in Dictionary	Python, Java	O(n l)*	O(t)	Medium	string, Trie, DFS, good trick, `google`, `amazon`, `fb`	AGAIN**** (1)
0722	Remove Comments	Python, Java	O(n)	O(k)	Medium	string, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN (1)
0734	Sentence Similarity	Python , Java	O(n + p)	O(p)	Easy	string, good basic, graph, `hash table`, `collections.defaultdict(set)`, `google`, `fb`	OK***** (5)
0751	IP to CIDR	Python, Java	O(n)	O(1)	Medium	string, 🔒, bit manipulation, largest CIDR block that fits, `ip`, `google`	AGAIN (not start*)
0758	Bold Words in String	Python, Java	O(n l)*	O(t)	Easy	string, 🔒, LC 616, variant of Add Bold Tag in String, `google`	AGAIN (not start)
0791	Custom Sort String	Python, Java	O(n)	O(1)	Medium	string, `good basic`, sort, counter, `amazon`, `fb`, `google`, `uber`	AGAIN************ (7) (MUST)
0796	Rotate String	Python, Java	O(n)	O(1)	Easy	string, good basic, `KMP Algorithm`, `Rabin-Karp Algorithm`, `amazon`, `google`, `apple`, `microsoft`, `linkedin`	OK**** (2)(but again)
0804	Unique Morse Code Words	Python, Java	O(n)	O(n)	Easy	string, map letters to morse, hashset of transformations, `basic`, `google`, `apple`, `microsoft`	OK*
0806	Number of Lines To Write String	Python, Java	O(n)	O(1)	Easy	string, greedy line filling, `basic`, `google`	OK*
0809	Expressive Words	Python, Java	O(n + s)	O(l + s)	Medium	string, 2 pointers, group len, good basic, `google`, `amazon`, `fb`	AGAIN****** (2)
0816	Ambiguous Coordinates	Python, Java	O(n^4)	O(n)	Medium	string, trick, `google`	AGAIN**** (1)
0819	Most Common Word	Python, Java	O(m + n)	O(m + n)	Easy	string, `regular expression`, `amazon`, `google`, `microsoft`	OK** (2)
0820	Short Encoding of Words	Python, Java	O(n)	O(t)	Medium	string, Trie, `amazon`	AGAIN (not start)
0824	Goat Latin	Python, Java	O(n + w^2)	O(l)	Easy	string, `string basic`, `fb`, `google`	OK
0828	Count Unique Characters of All Substrings of a Given String	Python, Java	O(n)	O(1)	Hard	string, LC 1248, count each char’s contribution (prev/next same char), dp, `amazon`, `google`	AGAIN*** (2)
0831	Masking Personal Information	Python, Java	O(1)	O(1)	Medium	string, `regular expression`	OK*
0833	Find And Replace in String	Python, Java	O(n + m)	O(n)	Medium	string, good basic, string op, hashmap, `google`, `amazon`, `fb`, `microsoft`, `linkedin`	AGAIN****** (3)
0848	Shifting Letters	Python, Java	O(n)	O(1)	Medium	string, `remainder`, `basic`, `amazon`, `fb`	AGAIN**
0859	Buddy Strings	Python, Java	O(n)	O(1)	Easy	string, compare differing positions, duplicate-char check, `trick`, `google`, `fb`	AGAIN*
0880	Decoded String at Index	Python, Java	O(n)	O(1)	Medium	string, `trick`, `amazon`	AGAIN (not start**)
0884	Uncommon Words from Two Sentences	Python, Java	O(m + n)	O(m + n)	Easy	string, `collections Counter`, `trick`, `google`, `amazon`, `fb`, `microsoft`	OK*
0890	Find and Replace Pattern	Python, Java	O(n l)*	O(1)	Medium	string, hashmap, pattern, LC 49, `google`, `amazon`, `apple`	AGAIN *** (3)
0893	Groups of Special-Equivalent Strings	Python, Java	O(n l)*	O(n)	Easy	string, sort even- and odd-indexed chars separately, hashset, `trick`, `fb`	AGAIN*
0916	Word Subsets	Python, Java	O(m + n)	O(1)	Medium	string, max char count across all words in b, Counter, `good trick`, `google`, `amazon`, `fb`	AGAIN (not start)
0917	Reverse Only Letters	Python, Java	O(n)	O(1)	Easy	string, `good basic`, `stack`, `pointer`, `google`, `amazon`, `apple`, `microsoft`	AGAIN**** (1)
0925	Long Pressed Name	Python, Java	O(n)	O(1)	Easy	string, `two pointer`, `basic`, `trick`, `google`	AGAIN*
0929	Unique Email Addresses	Python, Java	O(n l)*	O(n l)*	Easy	string, normalize local part (drop dots, cut at +), hashset, `basic`, `google`, `amazon`	OK
0939	Minimum Area Rectangle	Python, Java	O(n^2)	O(n)	Medium	string, hashmap, brute force, `google`, `array`, `math`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN !!! (2)
0942	DI String Match	Python, Java	O(n)	O(1)	Easy	string, good basic, 2 pointers, `google`, `amazon`, `microsoft`, `uber`	AGAIN*** (1)
0944	Delete Columns to Make Sorted	Python, Java	O(n l)*	O(1)	Easy	string, count columns that are not sorted, `basic`, `google`	AGAIN (not start)
0953	Verifying an Alien Dictionary	Python, Java	O(n l)*	O(1)	Easy	string, map chars to the alien order then compare adjacent words, `good basic`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode250`	AGAIN********** (3) (MUST)
0955	Delete Columns to Make Sorted II	Python, Java	O(n l)*	O(n)	Medium	string, LC 944, greedy column keeping, `good trick`, `google`	AGAIN (not start)
1119	Remove Vowels from a String	Python, Java	O(n)	O(n)	Easy	string, `amazon`	OK
4006	Count Valid Prefixes	Python, Java	O(n)	O(1)	Easy	string, prefix, good basic, LC weekly	OK
4043	Count Rotations With Exactly K Equal Adjacent Pairs	Python	O(n)	O(1)	Easy	string, cyclic pairs, a rotation only cuts ONE pair so score is C or C-1, brute force O(n^2) as V0, LC weekly	AGAIN(1)

Queue

#	Title	Solution	Time	Space	Difficulty	Note	Status
0239	Sliding Window Maximum	Python, Java	O(n)	O(k)	Hard	queue, sliding window, heap, deque, good trick, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN************ (6)
0281	Zigzag Iterator	Python, Java	O(n)	O(k)	Medium	queue, `good basic`, 🔒, `google`, `fb`, `amazon`, `apple`	AGAIN******* (5)
0346	Moving Average from Data Stream	Python, Java	O(1)	O(w)	Easy	queue, 🔒, `google`, `fb`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`	OK** (6)
0622	Design Circular Queue	Python, Java	O(1) per op	O(k)	Medium	queue, `good basic`, array, linked list, design, `circular queue`, `amazon`, `fb`, `apple`, `airbnb`, `microsoft`, `google`, `neetcode250`	AGAIN************ (3) (MUST)
0933	Number of Recent Calls	Python, Java	O(1) on average	O(w)	Easy	queue, deque, drop pings older than t - 3000, `basic`, `google`	AGAIN**

Math

#	Title	Solution	Time	Space	Difficulty	Note	Status
0007	Reverse Integer	Python, Java	O(1)	O(1)	Medium	math, `0x7FFFFFFF`, `amazon`, `apple`, `google`, `fb`, `microsoft`, `uber`, `bloomberg`, `neetcode150`	OK* (3)
0009	Palindrome Number	Python, Java	O(1)	O(1)	Easy	math, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`	OK
0012	Integer to Roman	Python, Java	O(1)	O(1)	Medium	math, `math basic`, `twitter`, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	AGAIN****** (4)
0013	Roman to Integer	Python, Java	O(n)	O(1)	Easy	math, good trick, map, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `neetcode250`	AGAIN***** (6)
0029	Divide Two Integers	Python, Java	O(logn)	O(1)	Medium	math, `binary search`, `trick`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN***** (3)
0050	Pow(x, n)	Python, Java	O(logn)	O(logn)	Medium	math, `good trick`, `amazon`, `fb`, recursion, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`	AGAIN****** (4)
0060	Permutation Sequence	Python, Java	O(n^2)	O(n)	Medium	math, `Cantor Ordering`, trick, `amazon`, `google`, `fb`, `apple`, `microsoft`	AGAIN*** (2)
0089	Gray Code	Python, Java	O(2^n)	O(1)	Medium	math, bit op, `amazon`, `google`, `microsoft`	AGAIN ********** (6)
0149	Max Points on a Line	Java	O(n^2)	O(n)	Hard	math, hashmap, `google`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN(1)
0166	Fraction to Recurring Decimal	Python, Java	O(n)	O(n)	Medium	math, hashmap remainder -> index to detect the repeating cycle, `good trick`, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN (not start)
0168	Excel Sheet Column Title	Python, Java	O(logn)	O(1)	Easy	math, trick, residual, AGAIN, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `neetcode250`	AGAIN****** (5)
0171	Excel Sheet Column Number	Python, Java	O(n)	O(1)	Easy	math, base-26 accumulation, LC 168, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN (not start)
0172	Factorial Trailing Zeroes	Python, Java	O(logn)	O(1)	Easy	math, `basic`, `iteration`, `recursion`, `amazon`, `fb`, `microsoft`, `bloomberg`	AGAIN* (2)
0223	Rectangle Area	Python, Java	O(1)	O(1)	Easy	math, area sum minus the overlap, `basic`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN
0258	Add Digits	Python, Java	O(1)	O(1)	Easy	math, digital root: 1 + (n - 1) % 9, `trick`, `google`, `amazon`, `apple`, `microsoft`	AGAIN
0263	Ugly Number	Python, Java	O(1)	O(1)	Easy	math, divide out 2, 3, 5, LC 264, `basic`, `amazon`, `apple`	OK* (2)
0273	Integer to English Words	Python, Java	O(logn)	O(1)	Hard	math, `amazon`, passed, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	not start
0292	Nim Game	Python, Java	O(1)	O(1)	Easy	math, LintCode, `google`	OK*
0319	Bulb Switcher	Python, Java	O(1)	O(1)	Medium	math, answer is floor(sqrt(n)) - only perfect squares have an odd divisor count, `good trick`, `fb`, `apple`, `microsoft`	AGAIN
0326	Power of Three	Python, Java	O(1)	O(1)	Easy	math, loop divide by 3, or 3^19 % n == 0, LC 231, LC 342, `basic`, `google`, `apple`	OK
0338	Counting Bits	Python, Java	O(n)	O(n)	Medium	math, dp, bit manipulation, `dp[i] = dp[i >> 1] + (i & 1)`, `good basic`, `google`, `amazon`, `fb`, `apple`, `uber`, `blind75`	OK
0343	Integer Break	Python, Java	O(n^2)	O(n)	Medium	math, max product, split into 3s, `trick`, `DP`, `google`, `amazon`, `fb`, `apple`, `neetcode250`	AGAIN********** (3)(MUST)
0365	Water and Jug Problem	Python, Java	O(logn)	O(1)	Medium	math, `Bézout's identity`, `google`, `microsoft`, `uber`	AGAIN (not start)
0372	Super Pow	Python, Java	O(n)	O(1)	Medium	math, modular fast power over the digit array	AGAIN
0382	Linked List Random Node	Python, Java	ctor: O(1), getRandom: O(n)	O(1)	Medium	math, `Reservoir Sampling`, `google`, `amazon`, `fb`	AGAIN (not start)
0386	Lexicographical Numbers	Python, Java	O(n)	O(1) excluding output	Medium	math, pre-order DFS over the 10-ary number trie, iterative, `good trick`, `google`, `amazon`, `microsoft`, `bloomberg`	AGAIN (not start)
0390	Elimination Game	Python, Java	O(logn)	O(1)	Medium	math, track head / step / remaining count, `good trick`, `amazon`, `bloomberg`	AGAIN (not start)
0398	Random Pick Index	Python, Java	ctor: O(1), pick: O(n)	O(1)	Medium	math, `Reservoir Sampling`, hashmap of value -> indices, `fb`, `google`, `amazon`, `microsoft`	OK* (4)
0400	Nth Digit	Python, Java	O(logn)	O(1)	Easy	math, count digits per length band then locate the number, `google`, `amazon`, `fb`	AGAIN
0413	Arithmetic Slices	Python, Java	O(n)	O(1)	Medium	math, dp, count consecutive runs with the same diff, `good basic`, `amazon`, `array`, `sliding window`, `fb`	OK*** (1) (but again)
0423	Reconstruct Original Digits from English	Python, Java	O(n)	O(1)	Medium	math, GCJ2016 - Round 1B	AGAIN (not start)
0441	Arranging Coins	Python, Java	O(logn)	O(1)	Easy	math, Binary Search on the row count, or the quadratic formula, `amazon`, `apple`	OK
0453	Minimum Moves to Equal Array Elements	Python, Java	O(n)	O(1)	Easy	math, incrementing n-1 elements equals decrementing 1, sum - n * min, `trick`, `amazon`, `apple`	AGAIN
0458	Poor Pigs	Python, Java	O(logn)	O(1)	Hard	math, information theory, (tests + 1) ^ pigs >= buckets, `good trick`	AGAIN
0469	Convex Polygon	Python, Java	O(n)	O(1)	Medium	math, 🔒, cross-product sign must stay consistent, `geometry`, `google`	AGAIN (not start)
0470	Implement Rand10() Using Rand7()	Python, Java	O(1)	O(1)	Medium	math, rejection sampling, LC 478, `good trick`, `google`, `apple`, `microsoft`, `uber`	AGAIN (not start)
0478	Generate Random Point in a Circle	Python, Java	O(1)	O(1)	Medium	math, rejection sampling or inverse transform with sqrt, `geometry`, `fb`	AGAIN (not start)
0497	Random Point in Non-overlapping Rectangles	Python, Java	ctor: O(n) pick: O(logn)	O(n)	Medium	math, prefix sum of rectangle areas + binary search, `good trick`, `google`	AGAIN (not start)
0504	Base 7	Python, Java	O(logn)	O(logn)	Easy	math, base conversion, good basic, recursion, `google`	AGAIN******** (1)
0517	Super Washing Machines	Python, Java	O(n)	O(1)	Hard	math, max of (max deficit, max single surplus), `greedy`, `amazon`, `array`, `microsoft`	AGAIN (not start)
0519	Random Flip Matrix	Python, Java	ctor: O(1) pick: O(1) reset: O(n)	O(n)	Medium	math, hashmap-based virtual Fisher-Yates swap, `good trick`, `google`	AGAIN (not start)
0528	Random Pick with Weight	Python, Java	O(logn)	O(n)	Medium	math, good basic, binary search, prefix sum, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN**** (1)
0537	Complex Number Multiplication	Python, Java	O(1)	O(1)	Medium	math, `amazon`	OK (3)
0553	Optimal Division	Python, Java	O(n)	O(1)	Medium	math, string, `amazon`	OK* (4)
0573	Squirrel Simulation	Python, Java	O(n)	O(1)	Medium	math, 🔒	AGAIN (not start)
0592	Fraction Addition and Subtraction	Python, Java	O(nlogx)	O(n)	Medium	math, parse signed fractions, reduce with gcd / lcm	AGAIN
0593	Valid Square	Python, Java	O(1)	O(1)	Medium	math, `google`, `fb`	AGAIN
0598	Range Addition II	Python, Java	O(p)	O(1)	Easy	math, answer is min(all a) * min(all b), `trick`, `amazon`	AGAIN
0625	Minimum Factorization	Python, Java	O(loga)	O(1)	Medium	math, 🔒	OK*
0628	Maximum Product of Three Numbers	Python, Java	O(n)	O(1)	Easy	math, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	OK (2)
0633	Sum of Square Numbers	Python, Java	O(sqrt© logc)*	O(1)	Easy	math, two pointers from 0 to sqrt©, or test each a, `basic`, `apple`, `linkedin`	OK*
0634	Find the Derangement of An Array	Python, Java	O(n)	O(1)	Medium	math, 🔒, `amazon`	AGAIN (not start)
0640	Solve the Equation	Python, Java	O(n)	O(n)	Medium	math, regular expression, `amazon`, `google`, `fb`	AGAIN*** (3)
0651	4 Keys Keyboard	Python, Java	O(n)	O(n)	Medium	math, 🔒, DP, `google`, `amazon`, `microsoft`	AGAIN (not start)
0672	Bulb Switcher II	Python, Java	O(1)	O(1)	Medium	math, only 6 distinct states after the first 3 lights, `trick`, `microsoft`	AGAIN (not start)
0728	Self Dividing Numbers	Python, Java	O(n)	O(1)	Easy	math, check that each digit divides the number, `basic`	AGAIN
0754	Reach a Number	Python, Java	O(logn)	O(1)	Medium	math, walk to the first triangular number >= target then fix parity, `good trick`, `google`, `amazon`	OK*
0775	Global and Local Inversions	Python, Java	O(n)	O(1)	Medium	math, trick, string, `amazon`, `google`	AGAIN** (not start) (3)
0779	K-th Symbol in Grammar	Python, Java	O(1)	O(1)	Medium	math, brute force, binary, recursion, `fb`, `amazon`, `google`, `apple`	AGAIN*** (1)
0781	Rabbits in Forest	Python, Java	O(n)	O(n)	Medium	math, group rabbits by their answer, ceil division, `good trick`	AGAIN (not start)
0789	Escape The Ghosts	Python, Java	O(n)	O(1)	Medium	math, compare Manhattan distances, `trick`, `google`	AGAIN
0800	Similar RGB Color	Python, Java	O(1)	O(1)	Easy	math, 🔒, `google`	AGAIN (not start)
0812	Largest Triangle Area	Python, Java	O(n^3)	O(1)	Easy	math, shoelace formula over all triples, `geometry`, `google`	AGAIN (not start)
0829	Consecutive Numbers Sum	Python, Java	O(sqrt(n))	O(1)	Medium	math, count factorizations n = k * m + k(k - 1) / 2, `good trick`, `google`, `amazon`, `uber`	AGAIN
0836	Rectangle Overlap	Python, Java	O(1)	O(1)	Easy	math, similar as 223. Rectangle Area, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`	AGAIN (2)
0858	Mirror Reflection	Python, Java	O(1)	O(1)	Medium	math, LCM / parity reasoning, `good trick`, `google`, `fb`	AGAIN (not start)
0866	Prime Palindrome	Python, Java	O(n^(1/2) (logn + n^(1/2)))*	O(logn)	Medium	math, generate palindromes then test primality, even-length ones divide by 11, `amazon`	AGAIN***
0867	Transpose Matrix	Java	O(m n)*	O(m n)*	Medium	math, duplicate of LC 868, `matrix`, `basic`, `array`, `simulation`, `amazon`, `apple`, `neetcode250`	AGAIN*
0883	Projection Area of 3D Shapes	Python, Java	O(n^2)	O(1)	Easy	math, xy = count of non-zero cells, yz = column max, zx = row max, `matrix`	AGAIN
0891	Sum of Subsequence Widths	Python, Java	O(nlogn)	O(1)	Hard	math, sort, each element contributes as max/min weighted by powers of 2, `amazon`	AGAIN (not start)
0907	Sum of Subarray Minimums	Python, Java	O(n)	O(n)	Medium	math, trick, LC 084, LC 2104, Ascending Stack, `amazon`, `array`, `dp`, `google`, `uber`	AGAIN**** (1)
0908	Smallest Range I	Python, Java	O(n)	O(1)	Easy	math, max(0, max - min - 2k), `basic`	OK* (2)
0910	Smallest Range II	Python, Java	O(nlogn)	O(1)	Medium	math, sort then try every split point, `greedy`, `good trick`, `apple`	AGAIN (not start)
0914	X of a Kind in a Deck of Cards	Python, Java	O(nlogn)	O(n)	Easy	math, gcd of all group counts must be >= 2, Counter, `google`	AGAIN (not start)
0963	Minimum Area Rectangle II	Python, Java	O(n^2)	O(n)	Medium	math, hashmap keyed by (center, diagonal length), `geometry`, `google`, `amazon`, `fb`	AGAIN (not start)
0970	Powerful Integers	Python, Java	O((logn)^2)	O®	Easy	math, `basic`, `amazon`	AGAIN* (2)
1015	Smallest Integer Divisible by K	Java	O(k)	O(1)	Medium	math, track remainder of 1, 11, 111 … mod k, pigeonhole, `google`, `apple`	AGAIN (not start)
1071	Greatest Common Divisor of Strings	Java	O(m + n)	O(1)	Easy	math, if s1 + s2 == s2 + s1 the answer is the prefix of length gcd(m, n), `good trick`, `amazon`, `neetcode250`	AGAIN (not start)
1342	Number of Steps to Reduce a Number to Zero	Python, Java	O(logn)	O(1)	Easy	math, `gra*`, `google`, `amazon`, `apple`, `microsoft`	ok
1492	The kth Factor of n	Python, Java	O(sqrt(n))	O(1)	Medium	math, `amazon`	AGAIN (not start)
1979	Find Greatest Common Divisor of Array	Python, Java	O(n + log(min))	O(1)	Easy	math, GCD	not start
2013	Detect Squares	Java	add: O(1), count: O(n)	O(n)	Medium	math, hashmap of point counts, iterate the diagonal point, `array`, `design`, `google`, `neetcode150`	not start
2028	Find Missing Observations	Python	O(n + m)	O(n)	Medium	math, distribute the missing sum evenly: feasible iff n <= need <= 6 * n, `divmod`, LC weekly	AGAIN (1)
2029	Stone Game IX	Python	O(n)	O(1)	Medium	math, game theory on counts mod 3, parity of c0 picks the rule, `good trick`, LC weekly	AGAIN (1)
2507	Smallest Value After Replacing With Sum of Prime Factors	Java	O(logn sqrt(n))*	O(1)	Medium	math, LC weekly	again (1)
2614	Prime In Diagonal	Java	O(n sqrt(M))*	O(1)	Easy	math, diagonal matrix, good basic, LC weekly	again**** (1)
2807	Insert Greatest Common Divisors in Linked List	Java	O(n log(maxV))*	O(1)	Medium	math, walk the list and insert gcd nodes, `linked list`, `basic`, `neetcode250`	OK
2961	Double Modular Exponentiation	Java	O(q logE)*	O(1)	Medium	math, weekly375	AGAIN (1)
3091	Apply Operations to Make Sum of Array Greater Than or Equal to k	Java	O(1)	O(1)	Medium	math, LC weekly	AGAIN (1)
3190	Find Minimum Operations to Make All Elements Divisible by Three	Java	O(n)	O(1)	Easy	math, LC weekly	OK
3194	Minimum Average of Smallest and Largest Elements	Java	O(nlogn)	O(1)	Easy	math, LC weekly, `array`, `two pointers`, `sort`	OK
3993	Maximum Value of an Alternating Sequence	Python, Java	O(1)	O(1)	Medium	math, LC weekly, good trick	again**** (1)

Scan Line

#	Title	Solution	Time	Space	Difficulty	Note	Status
1943	Describe the Painting	Java	O(nlogn)	O(n)	Medium	scan line, treeMap, delta, good basic, `google`, `array`, `hash table`, `sort`	AGAIN***** (1)(MUST)

Sort

#	Title	Solution	Time	Space	Difficulty	Note	Status
0075	Sort Colors	Python, Java	O(n)	O(1)	Medium	sort, Tri Partition, `two pointers`, `microsoft`, `fb`, `google`, `amazon`, `apple`, `uber`, `bloomberg`, `neetcode250`, `top100liked`	OK** (4)
0088	Merge Sorted Array	Python, Java	O(m + n)	O(1)	Easy	sort, `good basic`, merge, `two pointers`, `microsoft`, `amazon`, `fb`, `google`, `apple`, `uber`, `linkedin`, `bloomberg`, `neetcode250`	AGAIN************* (8) (MUST)
0128	Longest Consecutive Sequence	Python, Java	O(n)	O(n)	Medium	sort, 2 pointers, sliding window, `O(N)`, `amazon`, `array`, `hash table`, `union find`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN*************** (7) (MUST)
0147	Insertion Sort List	Python, Java	O(n^2)	O(1)	Medium	sort, `trick`, `amazon`, `apple`, `microsoft`	AGAIN* (2)
0148	Sort List	Python, Java	O(nlogn)	O(logn)	Medium	sort, `basic`, check `# 21 Merge Two Sorted Lists`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `top100liked`	AGAIN** (2)
0164	Maximum Gap	Java	O(n)	O(n)	Medium	sort, bucket sort / radix sort, pigeonhole on the gap, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK
0179	Largest Number	Python, Java	O(nlogn)	O(n)	Medium	sort, good basic, sort with lambda, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN************ (3)
0252	Meeting Rooms	Python, Java	O(nlogn)	O(n)	Easy	sort, LC 554, `uber`, `amazon`, `fb`, `google`, `microsoft`, `bloomberg`, `blind75`	OK*** (4) (but again)
0253	Meeting Rooms II	Python, Java	O(nlogn)	O(n)	Medium	sort, LC 2406, priority queue (min-heap), `scanning line`, `trick`, `booking.com`, `good`, `uber`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`, `blind75`	AGAIN************ (5) (MUST)
0274	H-Index	Python, Java	O(n)	O(n)	Medium	sort, Counting Sort, `good trick`, `fb`, `google`, `amazon`, `apple`, `bloomberg`	AGAIN***** (3)
0280	Wiggle Sort	Python, Java	O(n)	O(1)	Medium	sort, 🔒, `google`, `fb`, `amazon`, `microsoft`	OK*** (3)
0324	Wiggle Sort II	Python, Java	O(n) on average	O(1)	Medium	sort, variant of Sort Colors, Tri Partition, `google`, `amazon`, `fb`	AGAIN** (2)
0327	Count of Range Sum	Java	O(nlogn)	O(n)	Hard	sort, merge sort with counting, BIT, segment tree, `array`, `binary search`, `divide and conquer`, `google`, `amazon`	AGAIN (not start)
0347	Top K Frequent Elements	Python, Java	O(n)	O(n)	Medium	sort, HashMap, Heap, `yelp`, `amazon`, `fb`, GOOD basic, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN******** (4)
0406	Queue Reconstruction by Height	Python, Java	O(n^2)	O(n)	Medium	sort, `basic`, `trick`, `sort by key`, `insert`, `google`, next_big_val, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN********* (5)
0451	Sort Characters By Frequency	Python, Java	O(nlogn)	O(n)	Medium	sort, `collections.Counter(s).most_common`, `sorted(count_dict.items() with lambda`, good basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	OK* (4)
0493	Reverse Pairs	Java	O(nlogn)	O(n)	Hard	sort, merge sort with counting, or BIT, `good trick`, `array`, `binary search`, `divide and conquer`, `google`, `amazon`, `fb`, `microsoft`, `uber`	AGAIN (not start)
0692	Top K Frequent Words	Python, Java	O(n + klogk) on average	O(n)	Medium	sort, `good basic`, Quick Select, Heap, Bucket Sort, `heapq`, `yelp`, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`	OK***** (5)
0912	Sort an Array	Python, Java	O(nlogn)	O(n)	Medium	sort, merge sort, quick sort, `apple`, `amazon`, `microsoft`, `neetcode250`	AGAIN** (1)
0937	Reorder Data in Log Files	Python, Java	O(nlogn l)*	O(n l)*	Medium	sort, good basic, `string`, `amazon`, `google`, `apple`	OK**** (3)(again!!!)
0969	Pancake Sorting	Python, Java	O(n^2)	O(1)	Medium	sort, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN********** (4)
0973	K Closest Points to Origin	Python, Java	O(n) on average	O(1)	Medium	sort, good trick, sort with func, PQ, Heap, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `neetcode150`	OK***** (3)(but again)
0976	Largest Perimeter Triangle	Python, Java	O(nlogn)	O(1)	Easy	sort, sort descending then take the first valid triple, `greedy`, `basic`	OK* (2)
1057	Campus Bike	Java	O(m nlog(m * n))*	O(m n)*	Medium	sort, sort all (dist, worker, bike) triples or bucket by distance, `google`, `amazon`	AGAIN
1066	Campus Bike II	Java	O(m 2^n)*	O(2^n)	Medium	sort, bitmask dp over bikes, min cost assignment, `google`, `array`, `backtracking`, `amazon`	AGAIN
1152	Analyze User Website Visit Pattern	Python, Java	O(nlogn + u m^3)*	O(n + u m^3)*	Medium	sort, itertools.combinations, brute force, set, `amazon`	AGAIN***** (2) (not start)
1329	Sort the Matrix Diagonally	Java	O(m nlog(min(m, n)))*	O(m n)*	Medium	sort, group cells by (i - j), sort each diagonal, PQ, hashMap, `google`, `amazon`, `fb`, `microsoft`	AGAIN (not start)
1877	Minimize Maximum Pair Sum in Array	Java	O(nlogn)	O(1)	Medium	sort, good basic, `google`	AGAIN*** (1)
2021	Brightest Position on Street	Python, Java	O(nlogn)	O(n)	Medium	sort, LC 253 meeting room II, PQ, prefix, diff array, scanning line, trick, `amazon`	AGAIN*********** (3) (MUST)
2284	Sender With Largest Word Count	Java	O(n)	O(n)	Medium	sort, LC 347, hashmap, sort by (count, name), `good basic`, `array`, `string`	OK
2345	Finding the Number of Visible Mountains	Java	O(nlogn)	O(n)	Medium	sort, monotonic stack, hashmap, interval cover	AGAIN (not start)
2402	Meeting Rooms III	Java	O(nlogn)	O(n)	Hard	sort, LC 253, two heaps (free rooms / busy rooms), sort by start, `good trick`, `neetcode250`	AGAIN (not start)
2659	Make Array Empty	Java	O(nlogn)	O(n)	Hard	sort, BIT / sorted index scan, `good trick`, weekly_103	AGAIN (not start)

Two Pointers

#	Title	Solution	Time	Space	Difficulty	Note	Status
0019	Remove Nth Node From End of List	Python, Java	O(n)	O(1)	Medium	two pointers, good basic, MUST, `linked list`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `blind75`, `top100liked`	AGAIN********** (4) (MUST)
0042	Trapping Rain Water	Python, Java	O(n)	O(1)	Hard	two pointers, stack, prefix-suffix array, brute force, `amazon`, `apple`, `google`, `fb`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN******** (3)
0086	Partition List	Python, Java	O(n)	O(1)	Medium	two pointers, two dummy heads then splice, `linked list`, `good basic`, `amazon`, `fb`, `apple`, `microsoft`	OK*
0141	Linked List Cycle	Python, Java	O(n)	O(1)	Easy	two pointers, `basic`, `amazon`, `fb`, linked list, check #142, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK** (5)
0142	Linked List Cycle II	Python, Java	O(n)	O(1)	Medium	two pointers, linked list, check #141, `google`, `amazon`, `fb`, `apple`, `microsoft`, `linkedin`, `top100liked`	AGAIN****** (4) (again!)
0143	Reorder List	Python, Java	O(n)	O(1)	Medium	two pointers, LC 021, 206, 876, `good trick`, `inverse linkedlist`, `merge linkedlist`, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `blind75`	AGAIN************** (6) (MUST)
0167	Two Sum II - Input array is sorted	Python, Java	O(n)	O(1)	Medium	two pointers, dict, binary search, `good basic`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `neetcode150`	OK* (6)
0214	Shortest Palindrome	Java	O(n)	O(n)	Hard	two pointers, KMP failure function on s + ‘#’ + reverse(s), `good trick`, `string`, `rolling hash`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
0259	3Sum Smaller	Python, Java	O(n^2)	O(1)	Medium	two pointers, 🔒, LintCode, `good trick`, `google`, `fb`, check `#015 3 Sum`, check `#001 two sum`	AGAIN******** (4)
0283	Move Zeroes	Python, Java	O(n)	O(1)	Easy	two pointers, `basic`, `trick`, `shopee`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`, `top100liked`	AGAIN********* (6)
0344	Reverse String	Python, Java	O(n)	O(1)	Easy	two pointers, swap from both ends in place, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode250`	OK
0345	Reverse Vowels of a String	Python, Java	O(n)	O(1)	Easy	two pointers, `google`, `amazon`, `fb`, `apple`	OK** (1)
0349	Intersection of Two Arrays	Python, Java	O(m + n)	O(min(m, n))	Easy	two pointers, EPI, Hash, Binary Search, `fb`, `google`, `amazon`, `apple`, `microsoft`, `linkedin`	OK
0350	Intersection of Two Arrays II	Python, Java	O(m + n)	O(1)	Easy	two pointers, EPI, Hash, Binary Search, `good basic`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`	OK** (3)
0360	Sort Transformed Array	Python, Java	O(n)	O(1)	Medium	two pointers, `trick`, 🔒, `google`, `fb`	AGAIN*** (3)
0457	Circular Array Loop	Python, Java	O(n)	O(1)	Medium	two pointers, fast/slow pointers per start, same-direction check, `good trick`, `google`, `amazon`, `apple`, `microsoft`	AGAIN (not start)
0567	Permutation in String	Python, Java	O(n)	O(1)	Medium	two pointers, `sliding window`, counter, hashmap, `good basic`, `microsoft`, `fb`, `google`, `amazon`, `apple`, `uber`, `neetcode150`	AGAIN********* (8)(MUST)
0611	Valid Triangle Number	Python, Java	O(n^2)	O(1)	Medium	two pointers, sort then two pointers, count valid triples, `good trick`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	AGAIN (not start)
0777	Swap Adjacent in LR String	Python, Java	O(n)	O(1)	Medium	two pointers, L only moves left, R only moves right, relative order preserved, `good trick`, `google`	AGAIN (not start)
0826	Most Profit Assigning Work	Python, Java	O(mlogm + nlogn)	O(n)	Medium	two pointers, `trick`, `good basic`, `zip+sorted`, `google`, `amazon`, `uber`	OK*
0844	Backspace String Compare	Python, Java	O(m + n)	O(1)	Easy	two pointers, `good basic`, `stack`, `google`, `fb`, `amazon`, `apple`, `microsoft`, `uber`	OK* (4)
0876	Middle of the Linked List	Python, Java	O(n)	O(1)	Easy	two pointers, basic, `amazon`, `apple`, `google`, linkedlist, `fb`, `microsoft`	OK* (2)
0904	Fruit Into Baskets	Python, Java	O(n)	O(1)	Medium	two pointers, slide window, `google`, `array`, `hash table`, `amazon`, `apple`	AGAIN*** (1)
0930	Binary Subarrays With Sum	Python, Java	O(n)	O(1)	Medium	two pointers, `trick`, `array`, `hash table`, `sliding window`	AGAIN* (2) (not start)
0977	Squares of a Sorted Array	Python, Java	O(n)	O(1)	Easy	two pointers, two pointers from both ends, LC 88, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	OK
0986	Interval List Intersections	Python, Java	O(n)	O(1)	Medium	two pointers, scanning line, good basic, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN********* (1) (MUST)
1023	Camelcase Matching	Java	O(n)	O(1)	Medium	two pointers, dp, good basic, `google`, `amazon`	AGAIN****** (1)
1055	Shortest Way to Form String	Python, Java	O(n m)*	O(1)	Medium	two pointers, `google`, `fb`	again
1147	Longest Chunked Palindrome Decomposition	Java	O(n)	O(1)	Hard	two pointers, rolling hash, `google`	again (not start)
1151	Minimum Swaps to Group All 1’s Together	Python, Java	O(n)	O(1)	Medium	two pointers, good basic, Deque (Double-ended Queue), `amazon`, `array`, `sliding window`	AGAIN***** (not start )
1229	Meeting Scheduler	Java	O(n)	O(1)	Medium	two pointers, sort `amazon`, `google`, `amazon`, `apple`, `microsoft`	AGAIN***** (not start )
1498	Number of Subsequences That Satisfy the Given Sum Condition	Python	O(nlogn)	O(n)	Medium	two pointers, sort (only min + max matter), 2^(r - l) per left end, precomputed powers, `good trick`, `google`, `amazon`, `fb`	AGAIN(1)
1768	Merge Strings Alternately	Java	O(m + n)	O(m + n)	Easy	two pointers, merge two strings alternately then append the rest, `basic`, `google`, `uber`, `neetcode250`	OK
1963	Minimum Number of Swaps to Make the String Balanced	Python, Java	O(n)	O(1)	Medium	two pointers, good basic, greedy, stack, `amazon`, `fb`, `microsoft`	AGAIN******** (2)
3191	Minimum Operations to Make Binary Array Elements Equal to One I	Java	O(n)	O(1)	Medium	two pointers, greedy flip a window of 3, sliding window, LC 995, `good basic`, `array`, `bit manipulation`, `queue`	Again* (2)
3192	Minimum Operations to Make Binary Array Elements Equal to One II	Java	O(n)	O(1)	Medium	two pointers, LC 3191, greedy prefix flip with a running parity counter, `good trick`, `array`, `dp`	Again* (2)

Recursion

#	Title	Solution	Time	Space	Difficulty	Note	Status
0010	Regular Expression Matching	Python, Java	O(m n)*	O(m n)*	Hard	recursion, dp, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`	AGAIN (not start)
0095	Unique Binary Search Trees II	Python, Java	O(4^n / n^(3/2))	O(4^n / n^(3/2))	Medium	recursion, DP, # BSTs = combinations of left × right, `amazon`, `google`, `apple`, `backtracking`, `tree`, `fb`, `microsoft`	AGAIN***************** (1)(MUST)
0098	Validate Binary Search Tree	Python, Java	O(n)	O(h)	Medium	recursion, bfs, dfs, `BST`, `microsoft`, `amazon`, `fb`, `google`, `apple`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN****************** (11)
0100	Same Tree	Python, Java	O(n)	O(h)	Easy	recursion, dfs, bfs, `good basic`, `amazon`, `tree`, `google`, `fb`, `apple`, `microsoft`, `linkedin`, `bloomberg`, `blind75`	OK****** (5) (but again)
0104	Maximum Depth of Binary Tree	Python, Java	O(n)	O(h)	Easy	recursion, DFS, BFS, good basic, `amazon`, top down, bottom up, LC 111, `tree`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN************ (5)(MUST)
0105	Construct Binary Tree from Preorder and Inorder Traversal	Python, Java	O(n)	O(n)	Medium	recursion, `trick`, check # 106, `BST`, `microsoft`, `fb`, `google`, `amazon`, `apple`, `uber`, `bloomberg`, `blind75`, `top100liked`	AGAIN********* (9)
0106	Construct Binary Tree from Inorder and Postorder Traversal	Python, Java	O(n)	O(n)	Medium	recursion, `trick`, check # 105, `BST`, `microsoft`, `fb`, `google`, `amazon`	AGAIN******* (6)
0108	Convert Sorted Array to Binary Search Tree	Python, Java	O(n)	O(logn)	Easy	recursion, `good basic`, BST, build tree from sorted array, DFS, LC 109, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`, `top100liked`	AGAIN************* (2) (MUST)
0109	Convert Sorted List to Binary Search Tree	Python, Java	O(n)	O(logn)	Medium	recursion, `list`, `BST`, `good concept`, `fb`, `google`, `amazon`, `microsoft`, `bloomberg`	AGAIN*** (3)
0110	Balanced Binary Tree	Python, Java	O(n)	O(h)	Easy	recursion, `good trick`, LC 104, `dfs`, bfs, `amazon`, `fb`, `google`, top-down, bottom-up recursion, `tree`, `binary tree`, `apple`, `microsoft`, `bloomberg`, `neetcode150`	AGAIN************** (8)(MUST)
0111	Minimum Depth of Binary Tree	Python, Java	O(n)	O(h)	Easy	recursion, `good basic`, `dfs`, `BST`, `amazon`, `fb`, LC 104, `bfs`, `google`, `apple`, `microsoft`	AGAIN******** (5)
0114	Flatten Binary Tree to Linked List	Python, Java	O(n)	O(h)	Medium	recursion, good trick, Reverse Preorder DFS, `dfs`, `microsoft`, `fb`, `linked list`, `stack`, `tree`, `google`, `amazon`, `apple`, `uber`, `bloomberg`, `top100liked`	AGAIN*************** (6)(MUST)
0116	Populating Next Right Pointers in Each Node	Python, Java	O(n)	O(1)	Medium	recursion, good basic, bfs, dfs, tree, AGAIN, `fb`, `amazon`, `linked list`, `google`, `apple`, `microsoft`, `bloomberg`	AGAIN************ (6)
0117	Populating Next Right Pointers in Each Node II	Python, Java	O(n)	O(h)	Medium	recursion, good basic, prev node, `Populating Next Right Pointers in Each Node I`, bfs, linked list, `amazon`, `fb`, `google`, `tree`, `dfs`, `microsoft`, `bloomberg`	AGAIN************* (4)
0129	Sum Root to Leaf Numbers	Python, Java	O(n)	O(h)	Medium	recursion, path sum, dfs, good basic, `fb`, `tree`, `binary tree`, `google`, `amazon`, `apple`, `microsoft`	AGAIN******* (5)
0156	Binary Tree Upside Down	Python, Java	O(n)	O(1)	Medium	recursion, 🔒, `tree`, `dfs`, `binary tree`, `linkedin`	AGAIN (not start)
0241	Different Ways to Add Parentheses	Python, Java	O(n 4^n / n^(3/2))*	O(n 4^n / n^(3/2))*	Medium	recursion, complex, dp, Memoization, `google`, `amazon`, `fb`, `microsoft`	AGAIN (not start)
0298	Binary Tree Longest Consecutive Sequence	Python, Java	O(n)	O(h)	Medium	recursion, LC 437, good basic, prev node, bfs, dfs, tree, 🔒, `google`, `binary tree`, `amazon`, `fb`, `uber`	AGAIN *************** (6) (MUST)
0333	Largest BST Subtree	Python, Java	O(n)	O(h)	Medium	recursion, 🔒, dfs, post-order, return (isBST, min, max, size), LC 98, `dp`, `tree`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
0337	House Robber III	Python, Java	O(n)	O(h)	Medium	recursion, good trick, dp + dfs, tree DP, rob/not-rob state, LC 198, `amazon`, `google`, `fb`, `microsoft`, `uber`, `neetcode250`	AGAIN********** (3)(MUST)
0395	Longest Substring with At Least K Repeating Characters	Python, Java	O(26 n)*	O(1)	Medium	recursion, slide window, `DIVIDE AND CONQUER`, `good trick`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN************ (4)
0404	Sum of Left Leaves	Python, Java	O(n)	O(h)	Easy	recursion, tree, bfs, dfs, `amazon`, `google`, `fb`, `apple`	AGAIN**** (4)
0437	Path Sum III	Python, Java	O(n)	O(h)	Medium	recursion, LC 298, prefix sum, hashmap, dfs, path sum, `good trick`, `uber`, `amazon`, `fb`, `tree`, `binary tree`, `google`, `apple`,`top100liked`	AGAIN*********** (5) (MUST)
0501	Find Mode in Binary Search Tree	Java	O(n)	O(h)	Medium	recursion, dfs, bfs, LC 98, `tree`, `bst`, `google`, `amazon`	OK (1)
0544	Output Contest Matches	Python, Java	O(nlogn)	O(n)	Medium	recursion, 🔒, recursively pair first with last, string build, `good trick`, `google`	AGAIN
0549	Binary Tree Longest Consecutive Sequence II	Python, Java	O(n)	O(h)	Medium	recursion, 🔒, `tree`, `dfs`, `binary tree`, `google`, `amazon`, `fb`, `apple`	AGAIN (not start)
0669	Trim a Binary Search Tree	Python, Java	O(n)	O(h)	Medium	recursion, good basic, BST trim, dfs, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN*********** (6)(MUST)
0671	Second Minimum Node In a Binary Tree	Python, Java	O(n)	O(h)	Easy	recursion, dfs, tree, `binary tree`, `google`, `microsoft`, `uber`, `linkedin`	OK* (2)
0753	Cracking the Safes	Java	O(k^n n)*	O(k^n n)*	Hard	recursion, de Bruijn sequence, Hierholzer / dfs over states, `google`, `string`, `graph`, `apple`	AGAIN (not start)
1145	Binary Tree Coloring Game	Java	O(n)	O(h)	Medium	recursion, tree, color, `google`, `dfs`, `binary tree`	AGAIN***** (2)

Binary Search

#	Title	Solution	Time	Space	Difficulty	Note	Status
0033	Search in Rotated Sorted Array	Python, Java	O(logn)	O(1)	Medium	binary search, LC 153, 852, `good basic`, check `# 81 Search in Rotated Sorted Array II`, rotation array, `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN************ (6) (MUST)
0034	Find First and Last Position of Element in Sorted Array	Python, Java	O(logn)	O(1)	Medium	binary search, `amazon`, `fb`, `google`, `apple`, `uber`, `microsoft`, `linkedin`, `bloomberg`, `top100liked`	AGAIN************** (4) (MUST)
0034	Search for a Range	Python, Java	O(logn)	O(1)	Medium	binary search, duplicate of LC 34, lower bound + upper bound binary search, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `top100liked`	AGAIN*
0035	Search Insert Position	Python, Java	O(logn)	O(1)	Medium	binary search, LC 436, binary search on left, good basic, `google`, `amazon`, `fb`, `apple`, `bloomberg`, `neetcode250`, `top100liked`	AGAIN************ (2) (MUST)
0069	Sqrt(x)	Python, Java	O(logn)	O(1)	Medium	binary search, math, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode250`	OK* (4)
0074	Search a 2D Matrix	Python, Java	O(logm + logn)	O(1)	Medium	binary search, binary search in 2D array, flatten matrix, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`, `top100liked`	OK**** (BUT AGAIN)(3)
0081	Search in Rotated Sorted Array II	Python, Java	O(logn)	O(1)	Medium	binary search, check `# 33 Search in Rotated Sorted Array` first, `array`, `fb`, `amazon`, `linkedin`, `google`, `apple`, `microsoft`, `bloomberg`, `neetcode250`	OK***** (6)
0153	Find Minimum in Rotated Sorted Array	Python, Java	O(logn)	O(1)	Medium	binary search, LC 33, ascending array, good basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `blind75`, `top100liked`	AGAIN**************** (10)(MUST)
0154	Find Minimum in Rotated Sorted Array II	Java	O(logn)	O(1)	Medium	binary search, LC 153, `google`, `amazon`, `fb`, `microsoft`, `uber`	AGAIN (not start)
0162	Find Peak Element	Python, Java	O(logn)	O(1)	Medium	binary search, good trick, recursive, iterative binary search, `microsoft`, `google`, `fb`, `amazon`, `apple`, `uber`, `bloomberg`	AGAIN********** (6)
0222	Count Complete Tree Nodes	Python, Java	O((logn)^2)	O(logn)	Easy	binary search, `google`, tree, `amazon`, `fb`, `microsoft`	OK (again)
0275	H-Index II	Python, Java	O(logn)	O(1)	Medium	binary search, similar as `# 274 H-Index`, `fb`, `google`	AGAIN**** (3)
0278	First Bad Version	Python, Java	O(logn)	O(1)	Easy	binary search, `good basic`, LintCode, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`	OK*** (5) (MUST)
0300	Longest Increasing Subsequence	Python, Java	O(nlogn)	O(n)	Medium	binary search, Patience Sorting, `DP good basic`, LintCode, 1D DP, LIS, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `blind75`, `top100liked`	AGAIN******************* (13) (MUST)
0315	Count of Smaller Numbers After Self	Python, Java	O(nlogn)	O(n)	Hard	binary search, BST, BIT, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	again*
0367	Valid Perfect Square	Python, Java	O(logn)	O(1)	Easy	binary search, good basic, similar as `# 69 Sqrt(x)`, `google`, `amazon`, `fb`, `microsoft`, `linkedin`	OK* (3)
0374	Guess Number Higher or Lower	Python, Java	O(logn)	O(1)	Easy	binary search, classic binary search on the guess API, `good basic`, `google`, `amazon`, `apple`, `neetcode250`	OK*
0410	Split Array Largest Sum	Python, Java	O(nlog(sum))	O(1)	Hard	binary search, `google`, LC 1231, 1552, `amazon`, `fb`, `apple`, `uber`, `neetcode250`	AGAIN (not start)
0436	Find Right Interval	Python, Java	O(nlogn)	O(n)	Medium	lower bound / binary search, LC 35, good basic, `google`, `amazon`	AGAIN********** (3) (MUST)
0475	Heaters	Python, Java	O((m + n) logn)*	O(1)	Easy	binary search, sort houses and heaters, binary search the nearest heater, two pointers, `google`	AGAIN (not start)
0540	Single Element in a Sorted Array	Python, Java	O(logn)	O(1)	Medium	binary search, binary search on even indices, pair-XOR check, `good trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK*
0564	Find the Closest Palindrome	Java	O(n)	O(n)	Hard	binary search, n = number of digits, build 5 palindrome candidates around the prefix, `google`, `math`, `string`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN(not start)
0658	Find K Closest Elements	Python, Java	O(logn + k)	O(1)	Medium	binary search, `good trick`, PQ, binary search find window start point, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`	AGAIN ********************** (9) (MUST)
0704	Binary Search	Python	O(logn)	O(1)	Easy	binary search, the closed-interval template, `while l <= r`, `basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`, `neetcode250`	AGAIN(1)
0744	Find Smallest Letter Greater Than Target	Python, Java	O(logn)	O(1)	Easy	binary search, upper bound binary search with wraparound, `basic`, `amazon`, `linkedin`	OK*
0774	Minimize Max Distance to Gas Station	Python, Java	O(nlog(maxD / eps))	O(1)	Hard	binary search, binary search on a real-valued answer, PQ, `google`	AGAIN***** (1)
0852	Peak Index in a Mountain Array	Python, Java	O(logn)	O(1)	Medium	binary search, LC 162, LC 33, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN****** (2)
0875	Koko Eating Bananas	Python, Java	O(nlogr)	O(1)	Medium	binary search, left boundary, good basic, `google`, `amazon`, `fb`, `apple`, `neetcode150`	AGAIN******* (4)(MUST)
0894	All Possible Full Binary Trees	Python, Java	O(n 4^n / n^(3/2))*	O(n 4^n / n^(3/2))*	Medium	binary search, dfs + memoization, Catalan number, only odd n has a full binary tree, `dp`, `recursion`, `google`, `amazon`, `apple`	AGAIN (not start)
0911	Online Election	Python, Java	ctor: O(n) query : O(logn)	O(n)	Medium	binary search, prefix leader array + binary search on the query time, `good basic`, `google`, `apple`	AGAIN (not start)
0981	Time Based Key-Value Store	Python, Java	set: O(1), get: O(logn)	O(n)	Medium	binary search, dict, treeMap, floorKey, sort, `apple`, `microsoft`, `amazon`, `google`, `fb`, `uber`, `neetcode150`	AGAIN****** (2)
1011	Capacity To Ship Packages Within D Days	Python, Java	O(nlog(sum))	O(1)	Medium	binary search, good trick, `amazon`, `apple`, `fb`, `microsoft`, `google`, `uber`, `neetcode250`	AGAIN****** (3)
1060	Missing Element in Sorted Array	Java	O(logn)	O(1)	Medium	binary search, brute force, good trick, `google`, `amazon`, `fb`, `apple`, `bloomberg`	AGAIN**** (2)
1095	Find in Mountain Array	Java	O(logn)	O(1)	Hard	binary search, LC 852 find the peak then binary search each side, MountainArray API, `good trick`, `google`, `amazon`, `apple`, `neetcode250`	AGAIN (not start)s
1150	Check If a Number Is Majority Element in a Sorted Array	Java	O(logn)	O(1)	Easy	binary search, lower + upper bound, count occurrences, `fb`	AGAIN**** (1)
1231	Divide Chocolate	Java	O(nlog(sum))	O(1)	Hard	binary search, `google`, LC 2616, Maximize Minimum, LC 410, `amazon`, `fb`	AGAIN***** (not start)
1283	Find the Smallest Divisor Given a Threshold	Java	O(nlog(max))	O(1)	Medium	binary search, binary search on the divisor, LC 875, `good basic`, `google`, `amazon`, `uber`	AGAIN***** (not start)
1292	Maximum Side Length of a Square with Sum Less than or Equal to Threshold	Python, Java	O(m nlog(min(m, n)))*	O(m n)*	Medium	binary search, 2D prefix-sum, good trick, `google`, `amazon`	AGAIN******* (2)
1482	Minimum Number of Days to Make m Bouquets	Java	O(nlog(max))	O(1)	Medium	binary search, binary search on the day, greedily count adjacent runs, `good basic`, `google`	AGAIN (not start)
1552	Magnetic Force Between Two Balls	Java	O(nlogn + nlog(max))	O(1)	Medium	binary search, LC 410, can distribute, `google`, `amazon`, `uber`	AGAIN (1)
1760	Minimum Limit of Balls in a Bag	Java	O(nlog(max))	O(1)	Medium	binary search, binary search on the penalty, ceil(count / limit) - 1 operations, `good trick`	AGAIN (1)
1889	Minimum Space Wasted From Packaging	Python, Java	O((m + n) logn)*	O(n)	Hard	binary search, heap, prefix sum, `amazon`	AGAIN (not start)
1891	Cutting Ribbons	Java	O(nlog(max))	O(1)	Medium	binary search, 🔒, binary search on the ribbon length, `good basic`, `google`, `fb`, `uber`	AGAIN (not start)
2009	Minimum Number of Operations to Make Array Continuous	Python, Java	O(nlogn)	O(n)	Hard	binary search, sliding window, dequeue, bisect.bisect_right, `amazon`, `uber`	AGAIN (not start)
2554	Maximum Number of Integers to Choose From a Range I	Java	O(n)	O(n)	Medium	binary search, hash set of banned values, greedily take the smallest, weekly 97	AGAIN (not start)
2594	Minimum Time to Repair Cars	Java	O(nlog(maxT))	O(1)	Medium	binary search, PQ, trick, weekly 100	AGAIN***** (1)
2616	Minimize the Maximum Difference of Pairs	Java	O(nlogn + nlog(max))	O(1)	Medium	binary search, LC weekly, good trick, Minimize the Maximum, LC 1231	AGAIN******* (1)
4008	Minimum Initial Strength to Defeat All Monsters	Python, Java	O(n + m + nlog(sum))	O(n)	Medium	binary search, LC weekly, good trick	AGAIN* (1)

Binary Search Tree

#	Title	Solution	Time	Space	Difficulty	Note	Status
0099	Recover Binary Search Tree	Python, Java	O(n)	O(h)	Medium	BST, good trick, BST swap, DFS, inorder, Morris traversal, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN******************** (5)(MUST)
0220	Contains Duplicate III	Python, Java	O(nlogk)	O(k)	Medium	BST, LC 219, sliding window with TreeSet or bucketing, `good trick`, `array`, `sort`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
0230	Kth Smallest Element in a BST	Python, Java	O(max(h, k))	O(min(h, k))	Medium	BST, good basic BST basic, DFS, BFS, STACK, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	OK********* (4)
0235	Lowest Common Ancestor of a Binary Search Tree	Python, Java	O(h)	O(1)	Medium	BST, recursion, iteration, good basic, `LCA`, check `# 236 Lowest Common Ancestor of a Binary Tree`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `blind75`	OK**************** (but again)(10)
0270	Closest Binary Search Tree Value	Python, Java	O(h)	O(1)	Easy	BST, `good basic`, 🔒, `microsoft`, `google`, `fb`, `amazon`, `linkedin`, `bloomberg`	OK***** (5)
0272	Closest Binary Search Tree Value II	Java	O(h + k)	O(h + k)	Hard	BST, `google`, `amazon`, `fb`, closest val, binary search, `linkedin`	AGAIN (1)
0285	Inorder Successor in BST	Python, Java	O(h)	O(1)	Medium	BST, dfs, good basic, 🔒, `amazon`, `fb`, `google`, `microsoft`	OK** (4)
0426	Convert Binary Search Tree to Sorted Doubly Linked List	Python, Java	O(n)	O(h)	Medium	BST, recursion, tree, `linked list`, `good basic` `UBER`, `lyft`, `amazon`, `google`, `fb`, `microsoft`, `uber`	AGAIN******* (5) (not start)
0449	Serialize and Deserialize BST	Python, Java	O(n)	O(h)	Medium	BST, LC 297, dfs, bfs, good trick, `serizlize deserizlize`, tree, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN************* (9) (MUST)
0450	Delete Node in a BST	Python, Java	O(h)	O(h)	Medium	BST, good trick, tree, dfs, LC 1325, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `neetcode250`	AGAIN***************** (9) (MUST !!!)
0510	Inorder Successor in BST II	Java	O(h)	O(1)	Medium	BST, parent, `google`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN** (1) (not start)
0530	Minimum Absolute Difference in BST	Python, Java	O(n)	O(h)	Easy	BST, LC 783, `google`, `apple`	AGAIN*
0700	Search in a Binary Search Tree	Python, Java	O(h)	O(h)	Easy	BST, good basic, recursion, iteration amazon, `google`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN*** (1)
0776	Split BST	Python, Java	O(h)	O(h)	Medium	BST, 🔒, recursive, iterative, DFS, split, trick, AGAIN, `amazon`, `google`, `fb`	AGAIN************ (9)(MUST)
0783	Minimum Distance Between BST Nodes	Python, Java	O(n)	O(h)	Easy	BST, LC 530, `google`, `amazon`	OK*
0968	Binary Tree Cameras	Python, Java	O(n)	O(h)	Hard	BST, node state, dfs, bottom up, post order, dp, greedy, `microsoft`, `amazon`, `google`, `fb`, `apple`	AGAIN************* (3)(MUST)
1022	Sum of Root To Leaf Binary Numbers	Python, Java	O(n)	O(h)	Easy	BST, good basic, LC 257, bst path, dfs, bfs, `amazon`, `binary tree`, `google`, `apple`	AGAIN******** (1) (MUST)
1382	Balance a Binary Search Tree	Python, Java	O(n)	O(n)	Medium	BST, LC 105, 106, inorder then rebuild, dfs, good trick, AVL tree, `amazon`, `fb`, `apple`	AGAIN******** (2)
1597	Build Binary Expression Tree From Infix Expression	Python, Java	O(n)	O(n)	Hard	BST, LC 224, recursive, iteration, stack, `amazon`, `google`, `string`	AGAIN*** (1)
1644	Lowest Common Ancestor of a Binary Search Tree 2	Python, Java	O(n)	O(h)	Medium	BST, LC 235, 236, dfs, `binary tree`, `google`, `amazon`, `fb`, `microsoft`	AGAIN (1)

Breadth-First Search

#	Title	Solution	Time	Space	Difficulty	Note	Status
0102	Binary Tree Level Order Traversal	Python, Java	O(n)	O(n)	Medium	bfs, `GOOD basic`, `dfs`, `uber`, `apple`, `amazon`, `fb`, LC 199, `google`, `microsoft`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN******* (8) (must)
0103	Binary Tree Zigzag Level Order Traversal	Python, Java	O(n)	O(n)	Medium	bfs, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	OK
0107	Binary Tree Level Order Traversal II	Python, Java	O(n)	O(n)	Medium	bfs, same as `# 102 Binary Tree Level Order Traversal`, `google`, `amazon`, `apple`, `microsoft`	OK* (3)
0126	Word Ladder II	Python, Java	O(n l^2)*	O(n l)*	Hard	bfs, complex, trick, dfs, dfs+bfs, check `# 127 Word Ladder`, `amazon`, `google`, `fb`, `microsoft`, `uber`, `linkedin`	AGAIN*** (3) (not start)
0127	Word Ladder	Python, Java	O(n d)*	O(d)	Hard	bfs, good basic, set, LC 126 Word Ladder II, `uber`, `amazon`, `microsoft`, `fb`, `google`, `apple`, `linkedin`, `bloomberg`, `neetcode150`	AGAIN**************** (12)(MUST)
0130	Surrounded Regions	Python, Java	O(m n)*	O(m n)*	Medium	bfs, `dfs`, `union find`, good basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN*********** (5)
0133	Clone Graph	Python, Java	O(n)	O(n)	Medium	bfs, good trick, LC 138, `graph`, `dfs`, `uber`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `linkedin`, `blind75`	AGAIN**************** (11) (MUST)
0207	Course Schedule	Python, Java	O(V + E)	O(E)	Medium	bfs, Topological Sort, LC 210, `good trick`, `dfs`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `blind75`, `top100liked`	AGAIN**************** (15) (MUST)
0210	Course Schedule II	Python, Java	O(V + E)	O(E)	Medium	bfs, Topological Sort, LC 207, dfs, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN********* (10) (again)
0261	Graph Valid Tree	Python, Java	O(V + E)	O(V + E)	Medium	bfs, `union find`, dfs, grpah, 🔒, `graph`, `google`, `amazon`, `fb`, `microsoft`, `linkedin`, `blind75`	AGAIN************* (12)(MUST)
0286	Walls and Gates	Python, Java	O(m n)*	O(g)	Medium	bfs, 🔒, `dfs`, `good basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN******** (8)
0310	Minimum Height Trees	Python, Java	O(n)	O(n)	Medium	bfs, good trick, `undirected` graph, topo sort, Kahn algo, `google`, `amazon`, `fb`, `apple`, `microsoft`, `neetcode250`	AGAIN******* (5)
0317	Shortest Distance from All Buildings	Java	O(m^2 n^2)*	O(m n)*	Hard	bfs, multi-source BFS, total Path, cnt matrix, good trick, `google`, `amazon`, `fb`, `microsoft`, `uber`	AGAIN*********** (1)(must)
0407	Trapping Rain Water II	Java	O(m nlog(m * n))*	O(m n)*	Hard	bfs, PQ, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
0429	N-ary Tree Level Order Traversal	Java	O(n)	O(n)	Medium	bfs, PQ, `google`, `amazon`, `microsoft`	AGAIN*** (1)
0433	Minimum Genetic Mutation	Python, Java	O(n b)*	O(b)	Medium	bfs, check `# 127 Word Ladder`, `good basic`, `google`, `amazon`, `uber`	AGAIN*** (3)
0444	Sequence Reconstruction	Python, Java	O(n + m)	O(n)	Medium	bfs, good trick, `Topological Sort`, `google`, `airbnb`, `array`, `graph`	AGAIN******* (4) (not start)
0490	The Maze	Python, Java	O(max(r, c) w)*	O(w)	Medium	bfs, `basic`, `dfs`, `amazon`, `fb`, `google`, `microsoft`, `uber`	AGAIN**** (5)
0499	The Maze III	Java	O(m n * max(m, n) * log(m * n))*	O(m n)*	Medium	bfs, Dijkstra with lexicographically smallest path, roll until a wall, `good trick`, `google`, `microsoft`	AGAIN (not start)
0505	The Maze II	Python, Java	O(max(r, c) wlogw)*	O(w)	Medium	bfs, Dijkstra, `google`, `fb`, `amazon`	AGAIN********* (7)(MUST)
0542	01 Matrix	Python, Java	O(m n)*	O(m n)*	Medium	bfs, multi-source BFS, BFS get min dist, `google`, LC 994, 1765, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN************* (MUST) (4)
0666	Path Sum IV	Python, Java	O(n)	O(n)	Medium	bfs, 🔒, encode (depth, position) into a hashmap then dfs, tree, `array`, `fb`	AGAIN* (3) (not start)
0675	Cut Off Trees for Golf Event	Python, Java	O((m n)^2)*	O(m n)*	Hard	bfs, good trick, tree, mult-source BFS, shortest path, `amazon`, `google`, `apple`	AGAIN**************** (3)(must)
0742	Closest Leaf in a Binary Tree	Python, Java	O(n)	O(n)	Medium	bfs, Graph, bfs+dfs, search, `good trick`, `amazon`, `google`, `fb`	AGAIN************** (7)(MUST)
0743	Network Delay Time	Python, Java	O(E logV)*	O(V + E)	Medium	bfs, Dijkstra, Bellman-Ford, shortest path from one source, `google`, `amazon`, `microsoft`, `uber`, `neetcode150`	AGAIN **** (3)
0752	Open the Lock	Python, Java	O(k n^k + d)*	O(k n^k + d)*	Medium	bfs, LC 863, `google`, `amazon`, `fb`, `apple`, `uber`, `neetcode250`	AGAIN (not start)
0787	Cheapest Flights Within K Stops	Python, Java	O(E logV)*	O(E)	Medium	bfs, `Dijkstra's algorithm`, dfs, graph, priority queue, `amazon`, `apple`, `google`, `airbnb`, `fb`, `microsoft`, `uber`, `bloomberg`, `neetcode150`	AGAIN****** (4)
0815	Bus Routes	Python, Java	O(V + E)	O(V + E)	Hard	bfs, shortest route, graph, `amazon`, `google`, good trick, `fb`, `uber`	AGAIN****** (3)
0864	Shortest Path to Get All Keys	Python, Java	O(m n * 2^k)*	O(m n * 2^k)*	Hard	bfs, Dijkstra, Permutations, `amazon`, `google`	AGAIN (not start)
0886	Possible Bipartition	Python, Java	O(V + E)	O(V + E)	Medium	bfs, LC 785, `graph`, dfs, `union find`, `fb`, `google`, `amazon`, `apple`, `microsoft`	AGAIN********** (6)
0934	Shortest Bridge	Python, Java	O(n^2)	O(n^2)	Medium	bfs, BFS+DFS, multi-src BFS, good trick, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN************* (2)
0967	Numbers With Same Consecutive Differences	Python, Java	O(2^n)	O(2^n)	Medium	bfs, `good trick`, `uber`	AGAIN** (3)
0994	Rotting Oranges	Python, Java	O(m n)*	O(m n)*	Medium	bfs, dp `amazon`, good trick, LC 542, `google`, `amazon`, `fb`, `apple`, `microsoft`, `neetcode150`, `top100liked`	AGAIN********* (MUST) (2)
1091	Shortest Path in Binary Matrix	Java	O(n^2)	O(n^2)	Medium	bfs, `google`, `amazon`, `fb`, `microsoft`, `uber`	AGAIN (not start)
1110	Delete Nodes And Return Forest	Python, Java	O(n)	O(n)	Medium	bfs, pre+post order DFS, 2 states, prune, tree, `google`, `array`, `hash table`, `amazon`, `fb`	AGAIN************ (4)(MUST)
1136	Parallel Courses	Python	O(V + E)	O(V + E)	Medium	bfs, Topological Sort, Kahn algo, BFS level == 1 semester, 🔒, LC 207, LC 210, `graph`, `google`	AGAIN (1)
1162	As Far from Land as Possible	Python, Java	O(n^2)	O(n^2)	Medium	bfs, muti-source bfs, good basic, `amazon`, `google`, `fb`, `microsoft`	AGAIN********* (3)(MUST)
1197	Minimum Knight Moves	Java	O(n^2)	O(n^2)	Medium	bfs, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK (1)
1530	Number of Good Leaf Nodes Pairs	Python, Java	O(n d^2)*	O(n)	Medium	bfs, DFS, node pair, graph, good trick, `tree`, `binary tree`, `google`	AGAIN************ (2)(MUST)
1730	Shortest Path to Get Food	Python, Java	O(m n)*	O(m n)*	Medium	bfs, shortest path, `amazon`, `google`	OK (2)
1765	Map of Highest Peak	Java	O(m n)*	O(m n)*	Medium	bfs, dp, LC 542, `google`, `microsoft`	again (1)(not start)
1905	Count Sub Islands	Python, Java	O(m n)*	O(m n)*	Medium	bfs, dfs, `amazon`	AGAIN (1)
2115	Find All Possible Recipes from Given Supplies	Java	O(n + e)	O(n + e)	Medium	bfs, dfs, topological sort, `google`, `array`, `hash table`, `string`	OK (2)
2684	Maximum Number of Moves in a Grid	Java	O(m n)*	O(m n)*	Medium	bfs, top-down dp, bottom-up dp, LC weekly 345, `array`, `matrix`	again (1)

Depth-First Search

#	Title	Solution	Time	Space	Difficulty	Note	Status
0112	Path Sum	Python, Scala, Java	O(n)	O(h)	Easy	dfs, `good concept`, `amazon`, recursion, `google`, `fb`, `apple`, `microsoft`, `linkedin`	AGAIN** (2)
0113	Path Sum II	Python, Java	O(n)	O(h)	Medium	dfs, backtrack, LC 112, `good basic`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`	AGAIN************ (8)(MUST)
0199	Binary Tree Right Side View	Python, Java	O(n)	O(h)	Medium	dfs, `good basic`, `bfs`, `apple`, `amazon`, `fb`, LC 102, `google`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	OK*** (6)
0200	Number of Islands	Python, Java	O(m n)*	O(m n)*	Medium	dfs, `bfs`, `good basic`, check `# 694, 711 Number of Distinct Islands`, `apple`, `goldman sachs`, `google`, `amazon`, `fb`, LC 305, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK****** (6)
0236	Lowest Common Ancestor of a Binary Tree	Python, Java	O(n)	O(h)	Medium	dfs, `trick`, EPI, `LCA`, LC 1644, 235, `apple`, `amazon`, `linkedin`, `fb`, `google`, `microsoft`, `uber`, `bloomberg`, `top100liked`	AGAIN************* (9)
0247	Strobogrammatic Number II	Python, Java	O(n^2 5^(n/2))*	O(n)	Medium	dfs, 🔒, check `#246 Strobogrammatic Number`, `good trick`, `google`, `fb`, `array`, `string`, `recursion`, `uber`	AGAIN******** (5)
0257	Binary Tree Paths	Python, Java	O(n h)*	O(h)	Easy	dfs, good basic, `apple`, `google`, `amazon`, `fb`, top down, bottom up, LC 112, 113, `microsoft`	AGAIN************ (MUST) (7)
0332	Reconstruct Itinerary	Python, Java	O(E logE)*	O(E)	Hard	dfs, Hierholzer algo, `yelp`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`	AGAIN* (3) (not start)
0339	Nested List Weight Sum	Python, Java	O(n)	O(h)	Easy	dfs, 🔒, `good basic`, `bfs`, `linkedin`, `fb`, `amazon`, `microsoft`, `uber`	AGAIN*** (3)
0364	Nested List Weight Sum II	Python, Java	O(n)	O(h)	Medium	dfs, 🔒, `linkedin`, `fb`	AGAIN*
0366	Find Leaves of Binary Tree	Python, Java	O(n)	O(h)	Medium	dfs, 🔒, `linkedin`, `google`, `amazon`, `apple`	AGAIN*
0399	Evaluate Division	Python, Java	O(q (V + E))*	O(V + E)	Medium	dfs, `union find`, `good trick`, `union find` `google`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`	AGAIN************** (9)(MUST)
0417	Pacific Atlantic Water Flow	Python, Java	O(m n)*	O(m n)*	Medium	dfs, 2 direction dfs, matrix, `microsoft`, `google`, `amazon`, `fb`, `apple`, `uber`, `blind75`	AGAIN** (3)
0464	Can I Win	Python, Java	O(n 2^n)*	O(2^n)	Medium	dfs, `DP`, `linkedin`, `math`, `bit manipulation`, `google`, `amazon`	AGAIN* (not start)
0491	Increasing Subsequences	Python, Java	O(n 2^n)*	O(n 2^n)*	Medium	dfs, `trick`, `dfs good trick`, `dp`, `yahoo`, `fb`, `array`, `hash table`, `backtracking`, `google`, `apple`	AGAIN***** (2)
0515	Find Largest Value in Each Tree Row	Python, Java	O(n)	O(h)	Medium	dfs, `good basic`, `linkedin`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN* (3)
0529	Minesweeper	Python, Java	O(m n)*	O(m n)*	Medium	dfs, bfs, recursive update, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`	AGAIN******** (6)
0547	Friend Circles	Python, Java	O(n^2)	O(n)	Medium	dfs, graph, Union Find, bfs, check `# 733 Flood Fill`, `bloomberg`, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN*** (3) (not start)
0547	Number of Provinces	Python, Java	O(n^2)	O(n)	Medium	dfs, bfs, graph, union find, good basic, `apple`, `amazon`, `google`, `fb`, `microsoft`, `uber`, `linkedin`	AGAIN************ (2) (MUST)
0582	Kill Process	Python, Java	O(n)	O(n)	Medium	dfs, 🔒, BFS, `good basic`, `google`, `amazon`, `microsoft`, `bloomberg`	AGAIN*********** (5) (MUST)
0638	Shopping Offers	Python, Java	O(n 2^n)*	O(n)	Medium	dfs, `google`, `array`, `dp`, `backtracking`, `amazon`, `fb`, `apple`	AGAIN (not start*)
0690	Employee Importance	Python, Java	O(n)	O(h)	Easy	dfs, BFS, `good basic`, `uber`, `google`, `amazon`	OK** (3)
0694	Number of Distinct Islands	Python, Java	O(m n)*	O(m n)*	Medium	dfs, LC200, LC711, path signature, good pattern, 🔒, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN************* (7) (MUST)
0695	Max Area of Island	Python, Java	O(m n)*	O(m n)*	Medium	dfs, primitives in java, `amazon`, `microsoft`, `linkedin`, `basic`, `google`, `fb`, `apple`, `bloomberg`, `neetcode150`	AGAIN* (3)
0711	Number of Distinct Islands II	Python, Java	O(m n * logn)*	O(m n)*	Hard	dfs, complex, check `# 200, 694 Number of Distinct Islands`, `amazon`	OK*** (3)
0721	Accounts Merge	Python , Java	O(nlogn)	O(n)	Medium	dfs, Disjoint Set Union (DSU), `Union Find`, `path compression`, `complex`, `fb`, `google`, `amazon`, `microsoft`, `apple`, `twitter`, `uber`, `linkedin`, `neetcode250`	AGAIN******* (4) (not start)
0733	Flood Fill	Python, Java	O(m n)*	O(m n)*	Easy	dfs, `fb`, `amazon`, `good basic`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`	OK**** (5)
0737	Sentence Similarity II	Python, Java	O(n + p)	O(p)	Medium	dfs, good basic, map, union find, dis-joint, `google`, `amazon`	AGAIN************* (4)(MUST)
0756	Pyramid Transition Matrix	Python, Java	O(a^b)	O(a^b)	Medium	dfs, dfs over the allowed triples with memo, hashmap of (a, b) -> tops, `string`, `backtracking`, `google`, `amazon`	AGAIN (3) (not start)
0785	Is Graph Bipartite?	Python, Java	O(V + E)	O(V)	Medium	dfs, LC 886, color, `graph`, bfs, `fb`, `amazon`, `google`, `apple`, `microsoft`, `linkedin`	AGAIN******************* (8)
0797	All Paths From Source to Target	Python, Java	O(n 2^n)*	O(n 2^n)*	Medium	dfs, `graph`, `dfs classics`, `good basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `bloomberg`	AGAIN** (3)
0802	Find Eventual Safe States	Python, Java	O(V + E)	O(V)	Medium	dfs, `Topological Sort`, graph, `google`, `amazon`	AGAIN********** (5)
0827	Making A Large Island	Java	O(m n)*	O(m n)*	Hard	dfs, union find(DSU), 2 pass DFS/BFS, complex, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN**** (1)
0841	Keys and Rooms	Python, Java	O(n + e)	O(n)	Medium	dfs, `google`, `bfs`, `good basic`, `amazon`	AGAIN*** (3)
0851	Loud and Rich	Python, Java	O(n + e)	O(n + e)	Medium	dfs, `amazon`, `defaultdict`, `good basic`	AGAIN*** (3)
0987	Vertical Order Traversal of a Binary Tree	Java	O(nlogn)	O(n)	Hard	dfs, LC 314, bfs, tree map, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	AGAIN (not start)
0988	Smallest String Starting From Leaf	Java	O(n h)*	O(h)	Medium	dfs, bfs, `google`, `apple`	AGAIN (not start)
0990	Satisfiability of Equality Equations	Python, Java	O(n a(n))*	O(1)	Medium	dfs, union find, `array`, `string`, `google`, `amazon`	AGAIN (not start)
1020	Number of Enclaves	Java	O(m n)*	O(m n)*	Medium	dfs, flood fill from the border then count what remains, LC 1254, `good basic`, `google`	AGAIN (1)
1087	Brace Explansion	Python, Java	O(n p)*	O(n p)*	Medium	dfs, bfs, prefix sum, backtrack, good trick, Cartesian product, `google`, `string`, `stack`, `amazon`	AGAIN************** (3)(MUST)
1192	Critical Connections in a Network	Python, Java	O(n + e)	O(n + e)	Hard	dfs, Tarjan’s algorithm, graph, `fb`, `amazon`, `google`, `apple`	AGAIN** (1) (not start)
1254	Number of Closed Islands	Java	O(m n)*	O(m n)*	Medium	dfs, bfs, flood, good trick, 2 pass approach, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN (1)**********
1376	Time Needed to Inform All Employees	Python	O(n)	O(n)	Medium	dfs, invert manager to children first, answer = slowest root-to-leaf path, iterative (n = 10^5), `tree`, `google`, `amazon`	AGAIN(1)
1466	Reorder Routes to Make All Paths Lead to the City Zero	Java	O(n)	O(n)	Medium	dfs, bfs, `google`, `amazon`	AGAIN (1)
1644	Lowest Common Ancestor of a Binary Tree II	Python, Java	O(n)	O(h)	Medium	dfs, LCA, LC 236, `microsoft`, `fb`, `google`, `amazon`	AGAIN (not start)
1650	Lowest Common Ancestor of a Binary Tree III	Python, Java	O(h)	O(h)	Medium	dfs, `parent node`, good trick, set, dict, LCA, LC 236, `amazon`, `google`, spotify m$, `fb`, `two pointers`, `tree`, `apple`, `microsoft`	AGAIN******** (2) (MUST)
1676	Lowest Common Ancestor of a Binary Tree IV	Python, Java	O(n)	O(h)	Medium	dfs, `multi node LCA`, LC 236, set, m$, `amazon`, `microsoft`	AGAIN********* (1) (MUST)
2049	Count Nodes With the Highest Score	Python, Java	O(n)	O(n)	Medium	dfs, trick, graph, tree, `google`	AGAIN**** (not start)
2316	Count Unreachable Pairs of Nodes in an Undirected Graph	Python, Java	O(n + e)	O(n + e)	Medium	dfs, bfs, union find, good trick	AGAIN******** (1)
2658	Maximum Number of Fish in a Grid	Java	O(m n)*	O(m n)*	Medium	dfs, bfs, weekly_103	AGAIN (1)
2685	Count the Number of Complete Components	Java	O(n + e)	O(n + e)	Medium	dfs, good trick, bfs, union find, LC weekly 345	AGAIN*** (2)
2872	Maximum Number of K-Divisible Components	Java	O(n)	O(n)	Hard	dfs, BFS, topological sort, good trick, post order	AGAIN*** (2)
3319	K-th Largest Perfect Subtree Size in Binary Tree	Java	O(nlogn)	O(n)	Medium	dfs, good trick, binary-tree, post order	AGAIN*** (2)
3965	Finish Time of Tasks I	Python, Java	O(n)	O(n)	Medium	dfs, max_small_val, LC bi-weekly	AGAIN******** (4)(MUST)
3997	Count Dominant Nodes in a Binary Tree	Python, Java	O(n)	O(h)	Medium	dfs, LC weekly	AGAIN*** (1)
4015	Weighted Sum of a Tree	Python, Java	O(n)	O(n)	Medium	dfs, LC weekly	AGAIN*** (1)

Backtracking

#	Title	Solution	Time	Space	Difficulty	Note	Status
0017	Letter Combinations of a Phone Number	Python, Java	O(n 4^n)*	O(n)	Medium	backtracking, dfs, `good trick`, `uber`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN************* (11) (MUST)
0022	Generate Parentheses	Python, Java	O(4^n / n^(3/2))	O(n)	Medium	backtracking, LC 20, good basic, stack, backtrac, Divide and Conquer, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	OK**************** (5) (but again, MUST)
0037	Sudoku Solver	Python, Java	O(9^m)	O(m)	Hard	backtracking, backtrack over the m empty cells, row/col/box bitsets, `google`, `amazon`, `uber`, `fb`, `apple`, `microsoft`	AGAIN(not start)
0039	Combination Sum	Python, Java	O(k n^k)*	O(k)	Medium	backtracking, `dfs`, `good basic`, `uber`, `airbnb`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	OK********* (7) (but again)
0040	Combination Sum II	Python, Java	O(k C(n, k))*	O(k)	Medium	backtracking, LC 39, avoud duplicated, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `neetcode150`	AGAIN******* (4) (MUST)
0046	Permutations	Python, Java	O(n n!)*	O(n)	Medium	backtracking, LC #77, 78, `good concept`, `microsoft`, `linkedin`, `amazon`, `fb`, `google`, `apple`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	OK*********** (4) (AGAIN, MUST)
0047	Permutations II	Python, Java	O(n n!)*	O(n)	Medium	backtracking, LC 46, avoid same layer duplicated, `apple`, `amazon`, `microsoft`, `fb`, `uber`, `linkedin`, `neetcode250`	AGAIN***** (MUST)
0051	N-Queens	Python, Java	O(n!)	O(n^2)	Hard	backtracking, matrix, `bitmask`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`, `top100liked`	AGAIN********* (2)(MUST)
0052	N-Queens II	Python, Java	O(n!)	O(n)	Hard	backtracking, matrix, `amazon`, `neetcode250`	AGAIN
0077	Combinations	Python, Java	O(k C(n, k))*	O(k)	Medium	backtracking, good trick, `google`, `amazon`, `fb`, `apple`, `microsoft`, `neetcode250`	OK************* (5) (but again, MUST)
0078	Subsets	Python, Java	O(n 2^n)*	O(n)	Medium	backtracking, `good concept`, similar as, dfs, `#90 Subsets II` , `uber`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN**************** (7) (MUST again!!!)
0079	Word Search	Python, Java	O(m n * 4^l)*	O(l)	Medium	backtracking, LC 212, `good trick`, `dfs`, `bloomberg`, `microsoft`, `amazon`, `fb`, `google`, `apple`, `uber`, `linkedin`, `blind75`, `top100liked`	AGAIN*************** (10) (MUST)
0090	Subsets II	Python, Java	O(n 2^n)*	O(n)	Medium	backtracking, good basic, check `# 078 Subsets`, dfs, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN********* (6)
0093	Restore IP Addresses	Python, Java	O(1)	O(1)	Medium	backtracking, good trick, recursive, IP address, `amazon`, `google`, `fb`, `apple`, `microsoft`	AGAIN****** (4)
0131	Palindrome Partitioning	Python, Java	O(n 2^n)*	O(n^2)	Medium	backtracking, dfs, good trick, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`,`neetcode150`, `top100liked`	AGAIN************** (9) (MUST)
0139	Word Break	Python, Java	O(n^2 l)*	O(n)	Medium	backtracking, dfs, `dp`, `good DP basic`, `uber`, `yahoo`, `amazon`, `google`, `fb`, `array`, `hash table`, `string`, `apple`, `microsoft`, `bloomberg`, `blind75`, `top100liked`	AGAIN********************** (9) (MUST)
0140	Word Break II	Python, Java	O(n 2^n)*	O(n 2^n)*	Hard	backtracking, good basic, LC 078, dfs, `dp`, `trick`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode250`	AGAIN******** (2)
0212	Word Search II	Python, Java	O(m n * 4^l)*	O(t)	Hard	backtracking, LC 208, LC 079, hashset, hashmap, trie, backtrack with trie, `amazon`, `fb`, `apple`, `twitter`, `uber`, `google`, `indeed`, `microsoft`, `blind75`	AGAIN********** (3)
0216	Combination Sum III	Python, Java	O(k C(n, k))*	O(k)	Medium	backtracking, LC 39, LC 40, pick k distinct numbers from 1…9, `google`, `amazon`, `microsoft`	AGAIN*
0254	Factor Combinations	Python, Java	O(sqrt(n) f)*	O(logn)	Medium	backtracking, 🔒, f = number of factor combinations, dfs from the smallest factor, `google`, `uber`, `linkedin`	AGAIN (not start)
0267	Palindrome Permutation II	Python, Java	O(n n!)*	O(n)	Medium	backtracking, 🔒, LC 266, permute half then mirror, `google`, `amazon`, `fb`, `uber`	AGAIN (not start*)
0282	Expression Add Operators	Python	O(4^n n)*	O(n)	Hard	backtracking, carry the last operand so `*` can be undone, leading-zero guard, `complex`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN(1)
0294	Flip Game II	Python, Java	O(n 2^n)*	O(2^n)	Medium	backtracking, 🔒, DP, Hash, `google`	AGAIN*
0301	Remove Invalid Parentheses	Python	O(2^n n)*	O(2^n n)*	Hard	backtracking, BFS level by level = minimum removals, LC 20, LC 921, dedupe the frontier, `good trick`, `google`, `amazon`, `fb`, `apple`, `uber`, `bloomberg`	AGAIN(1)
0320	Generalized Abbreviation	Python, Java	O(n 2^n)*	O(n)	Medium	backtracking, 🔒, abbreviate or keep each char, bit mask, dfs, `google`	AGAIN (not start*)
0425	Word Squares	Python	O(m 26^L * L)*	O(m L)*	Hard	backtracking, prefix map, row k is forced by column k, LC 212, `trie`, `good trick`, `google`	AGAIN(1)
0489	Robot Room Cleaner	Python, Java	O(m n)*	O(m n)*	Hard	backtracking, 🔒, `google`, `amazon`, `fb`, `microsoft`	AGAIN (not start)
0526	Beautiful Arrangement	Python, Java	O(n!)	O(n)	Medium	backtracking, backtrack with divisibility pruning, bitmask dp, `good trick`, `google`, `amazon`	AGAIN (not start*)
0676	Implement Magic Dictionary	Python, Java	build: O(t), search: O(26 l)*	O(t)	Medium	backtracking, Trie, DFS, `hash table`, `string`, `google`, `amazon`, `fb`, `microsoft`	AGAIN (not start)
0698	Partition to K Equal Sum Subsets	Python, Java	O(n 2^n)*	O(2^n)	Medium	backtracking, DP, Memoization, similar as `#416 Partition Equal Subset Sum, #473 Matchsticks to Square`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `linkedin`, `neetcode250`	AGAIN****** (2) (MUST)
0718	Maximum Length of Repeated Subarray	Python, Java	O(m n)*	O(min(m, n))	Medium	backtracking, DP, Hash, Binary Search, `array`, `google`, `amazon`, `apple`	AGAIN (not start*)
0784	Letter Case Permutation	Python, Java	O(n 2^n)*	O(n)	Medium	backtracking, dfs, recursion, `good trick`, `fb`, `amazon`, `apple`, `microsoft`	AGAIN****** (3)
0980	Unique Paths III	Python, Java	O(3^(m n))*	O(m n)*	Hard	backtracking, good trick, LC 62, 63, dfs, `amazon`, `google`, `fb`, `apple`, `microsoft`	AGAIN********** (3)
1219	Path with Maximum Gold	Python, Java	O(3^(m n))*	O(m n)*	Medium	backtracking, dfs, bfs, `google`, `amazon`, `apple`	AGAIN**** (1)

Dynamic Programming

#	Title	Solution	Time	Space	Difficulty	Note	Status
0044	Wildcard Matching	Python	O(m n)*	O(m n)*	Hard	dp, `2D dp`, wildcard, greedy two-pointer, `amazon`, `facebook`, `google`	AGAIN (1)
0053	Maximum Subarray	Python, Java	O(n)	O(1)	Medium	dp, MUST, brute force, Kadane algo, pre-sum array, `dp basic`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN**************** (8)
0062	Unique Paths	Python, Java	O(m n)*	O(n)	Medium	dp, `2D dp`, `basic`, `fb`, `google`, `apple`, `amazon`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	AGAIN********* (3)(MUST)
0063	Unique Paths II	Python, Java	O(m n)*	O(n)	Medium	dp, `trick`, LC 64, dfs + dp, `amazon`, `google`, `fb`, `apple`, `microsoft`, `bloomberg`, `neetcode250`	AGAIN*
0064	Minimum Path Sum	Python, Java	O(m n)*	O(n)	Medium	dp, Sum of grid values, Dijkstra, LC 1631, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `neetcode250`, `top100liked`	AGAIN******* (3)(MUST)
0070	Climbing Stairs	Python, Java	O(n)	O(1)	Easy	dp, Matrix Exponentiation, `recursion`, `apple`, `google`, `amazon`, `fb`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	OK* (2)
0072	Edit Distance	Python, Java	O(m n)*	O(m n)*	Medium	dp, `2D DP`, dp state, `apple`, `google`, `amazon`, `fb`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN(5)************ (MUST)
0091	Decode Ways	Python, Java	O(n)	O(1)	Medium	dp, `good basic`, `microsoft`, `uber`, `amazon`, `fb`, `google`, `apple`, `bloomberg`, `blind75`	AGAIN*********************** (6) (MUST)
0096	Unique Binary Search Trees	Python, Java	O(n^2)	O(n)	Medium	dp, Math, `fb`, `amazon`, `google`, `apple`, `microsoft`, `bloomberg`	AGAIN* (2) (not start)
0097	Interleaving String	Java, Python	O(m n)*	O(n)	Medium	dp, 1D, 2D DP, state machine, good trick, `google`, `amazon`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`	again************ (4)(MUST)
0115	Distinct Subsequences	Java	O(m n)*	O(n)	Hard	dp, 2D dp, good trick, needcode 150, `google`, `amazon`, `apple`, `neetcode150`	AGAIN******** (1)
0120	Triangle	Python, Java	O(m n)*	O(n)	Medium	dp, `amazon`, `google`, `apple`, `microsoft`, `bloomberg`	AGAIN* (not start) (2)
0123	Best Time to Buy and Sell Stock III	Python, Java	O(n)	O(1)	Hard	dp, `amazon`, `uber`, `apple`, `google`, `fb`, `microsoft`	AGAIN* (not start) (1)
0132	Palindrome Partitioning II	Python	O(n^2)	O(n^2)	Hard	dp, LC 131, palindrome table + min-cut per prefix in one pass, `2D dp`, `good trick`, `google`, `amazon`	AGAIN(1)
0152	Maximum Product Subarray	Python, Java	O(n)	O(1)	Medium	dp, Kadane algo, brute force, `google`, `amazon`, `linkedin`, `fb`, `apple`, `microsoft`, `uber`, `blind75`, `top100liked`	AGAIN***** (1)
0198	House Robber	Python, Java	O(n)	O(1)	Easy	dp, dp basic, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN*** (2)
0213	House Robber II	Python, Java	O(n)	O(1)	Medium	dp, good trick, LC 198, circular dp, `google`, `amazon`, `apple`, `microsoft`, `blind75`	AGAIN*************** (4)(MUST)
0221	Maximal Square	Python, Java	O(m n)*	O(n)	Medium	dp, EPI, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`	AGAIN** (3) (not start)
0256	Paint House	Python, Java	O(n)	O(1)	Medium	dp, `google`, 🔒, `amazon`, `apple`, `linkedin`	AGAIN (2)
0276	Paint Fence	Python, Java	O(n)	O(1)	Easy	dp, good basic, 2 state DP, 🔒, `google`	AGAIN*********(3)
0279	Perfect Squares	Python, Java	O(n sqrt(n))*	O(n)	Medium	dp, bfs, 0/1 nbounded knapsack, GOOD trick, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode250`, `top100liked`	AGAIN************ (3)(MUST)
0303	Range Sum Query - Immutable	Python, Java	ctor: O(n), lookup: O(1)	O(n)	Easy	dp, prefix sum, LC 304, `good basic`, `array`, `design`, `google`, `amazon`, `fb`, `bloomberg`	OK
0304	Range Sum Query 2D - Immutable	Python, Java	ctor: O(m n), lookup: O(1)*	O(m n)*	Medium	dp, prefix sum, NOTE: idx, `trick`, `fb`, `array`, `design`, `matrix`, `google`, `amazon`, `apple`, `microsoft`, `neetcode250`	AGAIN******** (6)
0309	Best Time to Buy and Sell Stock with Cooldown	Python, Java	O(n)	O(1)	Medium	dp, 2D dp, n x m array, good basic, `google`, `amazon`, `fb`, `apple`, `neetcode150`	AGAIN********* (1)(MUST)
0312	Burst Balloons	Java	O(n^3)	O(n^2)	Hard	dp, interval dp, think in reverse (which balloon bursts last), `good trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN (not start)
0322	Coin Change	Python, Java	O(n k)*	O(k)	Medium	dp, bfs, dfs, grab, `google`, `fb`, `apple`, `amazon`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `blind75`, `top100liked`	AGAIN****************** (7) (MUST)
0329	Longest Increasing Path in a Matrix	Java	O(m n)*	O(m n)*	Hard	dp, good trick, dfs+dp, 2D DP, topo sort, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN************* (3)(MUST)
0351	Android Unlock Patterns	Python, Java	O(9^2 2^9)*	O(9 2^9)*	Medium	dp, 🔒 Backtracking, `google`, `apple`	AGAIN (not start)
0357	Count Numbers with Unique Digits	Python, Java	O(n)	O(1)	Medium	dp, Backtracking, Math, `google`	AGAIN (not start)
0361	Bomb Enemy	Python, Java	O(m n)*	O(m n)*	Medium	dp, 🔒, `google`, `amazon`, `uber`	AGAIN* (2)
0363	Max Sum of Rectangle No Larger Than K	Java	O(m^2 nlogn)*	O(n)	Medium	dp, pre-sum. `google`, `array`, `binary search`, `matrix`, `google`, `apple`, `microsoft`	AGAIN* (not start)
0368	Largest Divisible Subset	Python, Java	O(n^2)	O(n)	Medium	dp, sort then LIS-style dp, backtrack the chain, `good trick`, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN (not start)
0375	Guess Number Higher or Lower II	Python, Java	O(n^3)	O(n^2)	Medium	dp, interval dp / minimax, pick the cost that minimizes the worst case, `good trick`, `google`	AGAIN (not start)
0377	Combination Sum IV	Python, Java	O(n t)*	O(t)	Medium	dp, LC 518, dp basic, `fb`, `google`, `amazon`, `apple`, `neetcode250`	AGAIN******** (3)
0403	Frog Jump	Python, Java	O(n^2)	O(n^2)	Hard	dp, dfs, bfs, Memoization dfs, `amazon`, `microsoft`, `google`, `fb`, `apple`	AGAIN (not start)
0416	Partition Equal Subset Sum	Python, Java	O(n s)*	O(s)	Medium	dp, good basic, 0/1 knapsack, backward, 1d, 2d dp, `fb`, `google`, `apple`, `amazon`, `microsoft`, `uber`, `neetcode150`, `top100liked`	AGAIN******************* (6) (MUST)
0418	Sentence Screen Fitting	Python, Java	O(r + n c)*	O(n)	Medium	dp, 🔒, `google`, `uber`	AGAIN (not start)
0467	Unique Substrings in Wraparound String	Python, Java	O(n)	O(1)	Medium	dp, longest consecutive substring ending at each letter, `good trick`, `apple`	AGAIN (not start)
0471	Encode String with Shortest Length	Python, Java	O(n^3) on average	O(n^2)	Medium	dp, 🔒, `google`, `amazon`, `microsoft`	AGAIN (not start)
0472	Concatenated Words	Python, Java	O(n l^2)*	O(n l)*	Hard	dp, `good trick`, trie+dfs, `dfs`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN******** (3)
0474	Ones and Zeroes	Python, Java	O(s m * n)*	O(m n)*	Medium	dp, good basic, 2D 0/1 knapsack, `google`, `amazon`	AGAIN***** (2) (not start)
0486	Predict the Winner	Python, Java	O(n^2)	O(n)	Medium	dp, `good trick`, 1d, 2d DP, `google`, `amazon`, `uber`	AGAIN********* (again)(MUST)
0494	Target Sum	Python, Java	O(n s)*	O(s)	Medium	dp, 2D dp, math, `fb`, `google`, `amazon`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN****** (1)
0509	Fibonacci Number	Python, Java	O(logn)	O(1)	Easy	dp, variant of Climbing Stairs, `Matrix Exponentiation`, Spotify, `google`, `amazon`, `fb`, `apple`, `microsoft`	OK**
0516	Longest Palindromic Subsequence	Python, Java	O(n^2)	O(n)	Medium	dp, good basic, 2D DP, backward+forward, forward+forward, `uber`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `linkedin`	AGAIN**************** (MUST)
0518	Coin Change 2	Python, Java	O(n amount)*	O(amount)	Medium	dp, `dp basic`, `good trick`, LC 322, 377, `google`, `fb`, `amazon`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN******** (4)
0552	Student Attendance Record II	Java	O(n)	O(1)	Medium	dp, `2d, 3d dp`, good trick, `google`, `uber`	AGAIN*********** (3)
0562	Longest Line of Consecutive One in Matrix	Python, Java	O(m n)*	O(n)	Medium	dp, 🔒, `google`	AGAIN (not start)
0576	Out of Boundary Paths	Python, Java	O(N m * n)*	O(m n)*	Medium	dp, `bfs`, `amazon`	AGAIN (not start)
0583	Delete Operation for Two Strings	Python, Java	O(m n)*	O(n)	Medium	dp, `google`	AGAIN (not start)
0639	Decode Ways 2	Java	O(n)	O(1)	Hard	dp, LC 91, state dp with the `*` wildcard, mod 1e9+7, `google`, `amazon`, `fb`, `microsoft`	AGAIN (1) (not start)
0650	2 Keys Keyboard	Python, Java	O(sqrt(n))	O(1)	Medium	dp, `dp basic`, `microsoft`, `google`, `amazon`	AGAIN*
0673	Number of Longest Increasing Subsequence	Python, Java	O(n^2)	O(n)	Medium	dp, `good trick`, `fb`, `google`, `amazon`	AGAIN********** (3)
0688	Knight Probability in Chessboard	Python, Java	O(k n^2)*	O(n^2)	Medium	dp, `dp basic`, `AGAIN`, `microsoft`, `goldman sachs`, `google`, `fb`, `amazon`, `apple`	AGAIN********* (5)
0712	Minimum ASCII Delete Sum for Two Strings	Python, Java	O(m n)*	O(n)	Medium	dp, LC 583, 2D dp on ASCII sums	AGAIN (not start)
0714	Best Time to Buy and Sell Stock with Transaction Fee	Python, Java	O(n)	O(1)	Medium	dp, AGAIN, `good basic`, `greedy`, `fb`, `google`, `amazon`, `bloomberg`	AGAIN******** (3)
0727	Minimum Window Subsequence	Java	O(m n)*	O(m n)*	Hard	dp, `google`, `amazon`, `fb`, `apple`, `bloomberg`	AGAIN (not start)
0740	Delete and Earn	Python, Java	O(n + k)	O(k)	Medium	dp, LC 198, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN********* (1)(MUST)
0746	Min Cost Climbing Stairs	Python, Java	O(n)	O(1)	Easy	dp, `good dp basic`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN**** (2)
0750	Number Of Corner Rectangles	Python, Java	O(n m^2)*	O(n m)*	Medium	dp, `fb`, `google`	AGAIN (3) (not start)
0764	Largest Plus Sign	Python, Java	O(n^2)	O(n^2)	Medium	dp, complex, `fb`, `google`, `uber`	AGAIN (not start) (2)
0788	Rotated Digits	Python, Java	O(logn)	O(logn)	Easy	dp, `Brute Force`, Memoization, `google`, `amazon`, `fb`	OK*
0790	Domino and Tromino Tiling	Python, Java	O(logn)	O(1)	Medium	dp, Matrix Exponentiation, `google`, `amazon`	AGAIN (not start)
0799	Champagne Tower	Python, Java	O(n^2)	O(n)	Medium	dp, simulate the poured volume flowing down each row, 2D dp, `google`	AGAIN
0801	Minimum Swaps To Make Sequences Increasing	Python, Java	O(n)	O(1)	Medium	dp, `amazon`, `fb`, `google`, `apple`	AGAIN***** (not start) (2)
0808	Soup Servings	Python, Java	O(1)	O(1)	Medium	dp, memoized probability dp, converges to 1 for large n, `trick`, `google`	AGAIN (not start)
0813	Largest Sum of Averages	Python, Java	O(k n^2)*	O(n)	Medium	dp, `google`, `amazon`, `apple`	AGAIN (not start)
0823	Binary Trees With Factors	Python, Java	O(n^2)	O(n)	Medium	dp, sort + hashmap dp, count trees keyed by root value, `amazon`	AGAIN (not start)
0837	New 21 Game	Python, Java	O(n)	O(n)	Medium	dp, trick, math, `google`, `apple`, `uber`	AGAIN (2) (not start)
0838	Push Dominoes	Python, Java	O(n)	O(n)	Medium	dp, `two pointers`, `google`, `amazon`	AGAIN (not start)
0871	Minimum Number of Refueling Stops	Java	O(nlogn)	O(n)	Hard	dp, PQ, good trick, `google`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN***** (1)
0877	Stone Game	Python, Java	O(n^2)	O(n)	Medium	dp, LC 486, math, game theory, variant of Predict the Winner, `google`, `amazon`, `apple`, `neetcode250`	AGAIN*** (1)
0926	Flip String to Monotone Increasing	Python, Java	O(n)	O(1)	Medium	dp, good trick, prefix idx VS str idx, prefix sum, `google`, `amazon`	AGAIN*************** (6)(MUST)
0931	Minimum Falling Path Sum	Python, Java	O(n^2)	O(1)	Medium	dp, `google`, good basic, `amazon`, `apple`	AGAIN******** (2)(MUST)
0935	Knight Dialer	Python, Java	O(logn)	O(1)	Medium	dp, Matrix Exponentiation, `google`, `microsoft`, `fb`, `amazon`, `apple`	AGAIN (not start)
0983	Minimum Cost For Tickets	Java	O(n)	O(n)	Medium	dp, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN (not start)
1000	Minimum Cost to Merge Stones	Python, Java	O(n^3 / k)	O(n^2)	Hard	dp, `amazon`, `google`	AGAIN (not start)
1025	Divisor Game	Java	O(1)	O(1)	Easy	dp, n % 2 == 0 wins, `math`, `good trick`, `google`, `amazon`, `uber`	AGAIN (not start)
1048	Longest String Chain	Java	O(n l^2)*	O(n)	Medium	dp, 1D dp, hashmap, string, good basic, `google`, `amazon`, `fb`, `microsoft`	AGAIN******** (1)(MUST)
1049	Last Stone Weight II	Python, Java	O(n s)*	O(s)	Medium	dp, good trick !!!, 0/1 knapsack, minimize abs(S1 - S2), LC 416, 494, `google`, `amazon`, `neetcode250`	AGAIN****** (1)
1137	N-th Tribonacci Number	Python, Java	O(n)	O(1)	Easy	dp, good basic, `amazon`, `fb`, `neetcode250`	AGAIN**
1140	Stone Game II	Java	O(n^3)	O(n^2)	Medium	dp, need_code_250, `google`, `neetcode250`	AGAIN**
1143	Longest Common Subsequence	Python, Java	O(m n)*	O(n)	Medium	dp, Memoization, 2D dp, `amazon`, `karat`, `google`, `fb`, `microsoft`, `uber`, `blind75`, `top100liked`	AGAIN******************** (6)(DP MUST)
1277	Count Square Submatrices with All Ones	Java	O(m n)*	O(1)	Medium	dp, `google`, `amazon`, `fb`, `microsoft`	AGAIN(1) (not start)
1312	Minimum Insertion Steps to Make a String Palindrome	Python, Java	O(n^2)	O(n)	Hard	dp, `amazon`, `google`, `apple`, `microsoft`	AGAIN (not start)
1335	Minimum Difficulty of a Job Schedule	Python, Java	O(d n^2)*	O(d n)*	Hard	dp, `amazon`, `google`, `uber`	not start
1406	Stone Game III	Java	O(n)	O(n)	Medium	dp, `amazon`, `google`, `neetcode250`	AGAIN (not start)
1617	Count Subtrees With Max Distance Between Cities	Java	O(n^2 2^n)*	O(n^2)	Hard	dp, enumerate subsets with a bitmask, tree diameter per subset, `complex`	AGAIN (not start)
1799	Maximize Score After N Operations	Python, Java	O(n^2 2^n)*	O(2^n)	Medium	dp, `amazon`	not start
2560	House Robber IV	Java	O(nlog(max))	O(1)	Medium	dp, binary search	AGAIN (not start)
2646	Minimize the Total Price of the Trips	Java	O(m n)*	O(n)	Hard	dp, dfs, LC weekly	not start AGAIN (1)
2765	Longest Alternating Subarray	Java	O(n)	O(1)	Easy	dp, `2 pointers`, good trick, `array`	AGAIN(1) *****
2767	Partition String Into Minimum Beautiful Substrings	Java	O(n^2)	O(n)	Medium	dp, dp over prefixes, powers of 5 written in binary	AGAIN(1)
3122	Minimum Number of Operations to Satisfy Conditions	Java	O(m n + n * 100)*	O(n 10)*	Medium	dp, LC weekly, PQ	Again (1)
3196	Maximize Total Cost of Alternating Subarrays	Java	O(n)	O(1)	Medium	dp, LC weekly	Again

Greedy

#	Title	Solution	Time	Space	Difficulty	Note	Status
0011	Container With Most Water	Python, Java	O(n)	O(1)	Medium	greedy, good basics, `two pointers`, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `blind75`, `top100liked`	OK*** (3) (but again !!)
0045	Jump Game II	Python, Java	O(n)	O(1)	Medium	greedy, `google`, `apple`, `fb`, `tesla`, `amazon`, `microsoft`, `uber`, `neetcode150`, `top100liked`	AGAIN******** (4) (MUST)
0055	Jump Game	Python, Java	O(n)	O(1)	Medium	greedy, good trick, backtrack, DP, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `blind75`, `top100liked`	AGAIN*********** (9)(MUST)
0084	Largest Rectangle in Histogram	Python, Java	O(n)	O(n)	Hard	greedy, brute force, good trick, `mono stack`, LC 085, `amazon`, `fb`, `array`, `google`, `apple`, `microsoft`, `uber`, `bloomberg`, `neetcode150`, `top100liked`	AGAIN******** (3)
0122	Best Time to Buy and Sell Stock II	Python, Java	O(n)	O(1)	Easy	greedy, compare with `#309 Best Time to Buy and Sell Stock with Cooldown` , `#714 Best Time to Buy and Sell Stock with Transaction Fee`, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode250`	again* (2)
0134	Gas Station	Python, Java	O(n)	O(1)	Medium	greedy, trick, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN****** (5)
0135	Candy	Python, Java	O(n)	O(n)	Hard	greedy, LC 123, boundary, array, `amazon`, `google`, `apple`, `microsoft`, `neetcode250`	AGAIN (2)
0218	The Skyline Problem	Python, Java	O(nlogn)	O(n)	Hard	greedy, brute force, swipe line, Priority Queue, Union Find, Divide-and-Conquer, `apple`, `microsoft`, `array`, `binary indexed tree`, `google`, `amazon`, `fb`, `uber`	AGAIN (not start)
0316	Remove Duplicate Letters	Python, Java	O(n)	O(1)	Medium	greedy, good trick, MONO stack, char, visited, LC 1081, `google`, `amazon`, `fb`, `apple`, `microsoft`	AGAIN********* (4)(MUST)
0319	Bulb Switcher	Python, Java	O(1)	O(1)	Medium	greedy, duplicate of the Math entry, answer is floor(sqrt(n)), `good trick`, `fb`, `apple`, `microsoft`	not start
0330	Patching Array	Python, Java	O(n)	O(1)	Hard	greedy, array, `amazon`, `google`, `uber`	AGAIN (not start)
0358	Rearrange String k Distance Apart	Python, Java	O(n)	O(k)	Hard	greedy, PQ, check LC 767, cooldown queue, good trick, `google`, `amazon`, `fb`	AGAIN*** (1)
0376	Wiggle Subsequence	Python, Java	O(n)	O(1)	Medium	greedy, count direction changes, greedy or dp, `good basic`, `amazon`, `apple`, `uber`	AGAIN*
0392	Is Subsequence	Python, Java	O(n)	O(1)	Easy	greedy, `basics`, 2 pointers, dp, `string`, `google`, `amazon`, `fb`, `uber`	AGAIN********* (1)(MUST)
0397	Integer Replacement	Python, Java	O(logn)	O(1)	Medium	greedy, `Recursion basics`, Math, `google`, `amazon`, `microsoft`	OK*
0402	Remove K Digits	Python, Java	O(n)	O(n)	Medium	greedy, LintCode, mono stack, str, good trick, `google`, `amazon`, `fb`, `microsoft`	AGAIN************* (4)(MUST)
0435	Non-overlapping Intervals	Python, Java	O(nlogn)	O(1)	Medium	greedy, good trick, inverval, LC 452, Line Sweep, `google`, `amazon`, `fb`, `apple`, `microsoft`, `blind75`	AGAIN**************** (10)(must)
0452	Minimum Number of Arrows to Burst Balloons	Python, Java	O(nlogn)	O(1)	Medium	greedy, sort, compare i-1 element, overlap, good basic, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN***** (3)
0455	Assign Cookies	Python, Java	O(nlogn + mlogm)	O(1)	Easy	greedy, sort both arrays then two pointers, `basic`, `amazon`, `apple`	OK*
0621	Task Scheduler	Python, Java	O(n)	O(1)	Medium	greedy, `trick`, PQ+queue, compare with 767, cool down, `fb`, `amazon`, `google`, `apple`, `microsoft`, `uber`, `neetcode150`	AGAIN********* (8)(MUST)
0646	Maximum Length of Pair Chain	Python, Java	O(nlogn)	O(1)	Medium	greedy, good trick, similar as `#435 Non-overlapping Intervals`, Line Sweep, `amazon`, `fb`, `apple`, `uber`, `bloomberg`	OK********** (5) (but again)
0649	Dota2 Senate	Python, Java	O(n)	O(n)	Medium	greedy, complex question, `neetcode250`	AGAIN (not start*)
0659	Split Array into Consecutive Subsequences	Python, Java	O(n)	O(n)	Medium	greedy, map, pq, dp, `google`, `uber`	AGAIN***** (1)
0672	Bulb Switcher II	Python, Java	O(1)	O(1)	Medium	greedy, duplicate of the Math entry, only 6 reachable states, `trick`, `bit manipulation`, `dfs`, `microsoft`	not start
0738	Monotone Increasing Digits	Python, Java	O(logn)	O(logn)	Medium	greedy, good trick, string, trick, `amazon`	AGAIN********* (4)
0763	Partition Labels	Python, Java	O(n)	O(1)	Medium	greedy, good trick, dict, sliding window, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `neetcode150`, `top100liked`	AGAIN******* (6) (AGAIN)
0765	Couples Holding Hands	Java	O(n)	O(n)	Hard	greedy, hashmap, union find, `google`, `fb`	AGAIN (not start)
0767	Reorganize String	Python, Java	O(n)	O(1)	Medium	greedy, LC 1054, compare with 621, PQ, hashmap, `good trick`, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `neetcode250`	AGAIN****************** (9) (MUST)
0861	Score After Flipping Matrix	Python, Java	O(r c)*	O(1)	Medium	greedy, greedy: make column 0 all ones, then maximize each column, `good trick`, `amazon`	AGAIN (not start*)
0870	Advantage Shuffle	Python, Java	O(nlogn)	O(n)	Medium	greedy, sort both then greedily assign the smallest winning card (Tian Ji horse racing), `good trick`, `fb`, `apple`	OK*
0881	Boats to Save People	Python, Java	O(nlogn)	O(n)	Medium	greedy, `good trick`, `google`, `amazon`, `neetcode250`	AGAIN* (2)
0948	Bag of Tokens	Python, Java	O(nlogn)	O(1)	Medium	greedy, Two Pointers, `google`	AGAIN*** (1) (not start)
0962	Maximum Width Ramp	Python, Java	O(n)	O(n)	Medium	greedy, Descending Stack, `array`, `two pointers`, `google`, `fb`, `apple`	AGAIN (not start)
0978	Longest Turbulent Subarray	Java	O(n)	O(1)	Medium	greedy, sliding window, `array`, `dp`, `amazon`, `bloomberg`, `neetcode250`	AGAIN (not start)
0984	String Without AAA or BBB	Java, Python	O(n)	O(n)	Medium	greedy, good basic, while, string builder, endsWith, PQ, `microsoft`	AGAIN***** (2)
1024	Video Stitching	Python, Java	O(nlogn)	O(1)	Medium	greedy, Spotify, `google`, `amazon`	AGAIN (not start)
1102	Path With Maximum Minimum Value	Python, Java	O(m nlog(m * n))*	O(m n)*	Medium	greedy, dfs, dp, `amazon`, `array`, `binary search`, `google`, `fb`	not start
1375	Bulb Switcher III	Python, Java	O(n)	O(1)	Medium	greedy, queue, array, `gra*`, `amazon`, `microsoft`	AGAIN*** (1)
1380	Lucky Numbers in a Matrix	Java	O(m n)*	O(m + n)	Easy	greedy, intersect the row minimums with the column maximums, `matrix`, `basic`, `array`, `apple`	AGAIN (1)
1546	Maximum Number of Non-Overlapping Subarrays With Sum Equals Target	Python, Java	O(n)	O(n)	Medium	greedy, prefix + greedy, good trick, `google`, `microsoft`	AGAIN*** (1)
1648	Sell Diminishing-Valued Colored Balls	Python, Java	O(nlogn)	O(1)	Medium	greedy, trick, sorting, heapq, binary search, `amazon`	AGAIN*** (2) (not start)
1710	Maximum Units on a Truck	Python, Java	O(nlogn)	O(1)	Easy	greedy, sort, `amazon`, `apple`	AGAIN******** (3) (MUST)
1791	Find Center of Star Graph	Java	O(1)	O(1)	Easy	greedy, degree cnt, `graph`	AGAIN (1)
1851	Minimum Interval to Include Each Query	Java	O(nlogn + qlogq)	O(n + q)	Hard	greedy, needcode 150, PQ, interval, sort, scan line, Segment Tree, `google`, `array`, `binary search`, `neetcode150`	AGAIN************** (1)
1871	Jump Game VII	Java	O(n)	O(n)	Medium	greedy, bfs, `string`, `dp`, `sliding window`, `google`, `amazon`, `neetcode250`	AGAIN (not start)
1899	Merge Triplets to Form Target Triplet	Java	O(n)	O(1)	Medium	greedy, sort, `amazon`, `google`, `neetcode150`	AGAIN(1) (not srart)
2126	Destroying Asteroids	Java	O(nlogn)	O(1)	Medium	greedy, sort, `google`	AGAIN(1) (not srart)
2279	Maximum Bags With Full Capacity of Rocks	Java	O(nlogn)	O(n)	Medium	greedy, sort	AGAIN (1)
2591	Distribute Money to Maximum Children	Java	O(1)	O(1)	Easy	greedy, LC weekly	AGAIN (1)
2643	Row With Maximum Ones	Java	O(m n)*	O(1)	Easy	greedy, count ones per row, `matrix`, `basic`, `array`	AGAIN(1) (not srart)
2645	Minimum Additions to Make Valid String	Java	O(n)	O(1)	Medium	greedy, string	AGAIN(1) (not srart)
2656	Maximum Sum With Exactly K Elements	Java	O(n)	O(1)	Easy	greedy, weekly_103	AGAIN(1) (not srart)
2960	Count Tested Devices After Test Operations	Java	O(n)	O(1)	Easy	greedy, running count of tested devices acts as the decrement, `good trick`, `array`, `simulation`, `counting`	AGAIN(1) (not srart)
3120	Count the Number of Special Characters I	Java	O(n)	O(1)	Easy	greedy, hashset of seen chars, require both cases, LC 3121, `basic`, `string`	AGAIN(1) (not srart)
3689	Maximum Total Subarray Value I	Java	O(n)	O(1)	Medium	greedy, math, brute force	OK
3690	Split and Merge Array Transformation	Java	O(n! n^4)*	O(n! n)*	Medium	greedy, bfs dfs, `array`, `hash table`	AGAIN (not start)
3691	Maximum Total Subarray Value II	Java	O((n + k) logn)*	O(nlogn)	Hard	greedy, brute force, tree	AGAIN
3994	Transform Binary String Using Subsequence Sort	Python, Java	O(n)	O(1)	Medium	greedy, brute force, LC weekly	AGAIN*****(1)
3998	Transform Binary String Using Subsequence Sort	Python, Java	O(n m)*	O(n)	Medium	greedy, brute force, prefix, LC weekly	AGAIN
4040	Minimum Operations to Form Subset Sum I	Python	O(n sum * logx)*	O(sum)	Medium	dp, group 0/1 knapsack, per-element (value, cost) options, x2 / x//2 chains, LC weekly	AGAIN(1)

Graph

#	Title	Solution	Time	Space	Difficulty	Note	Status
0269	Alien Dictionary	Python, Java	O(n l)*	O(1)	Hard	graph, good trick, dfs, bfs, Topologicals sort, `fb`, `google`, `microsoft`, `airbnb`, `uber`, `amazon`, `apple`, `bloomberg`, `blind75`	AGAIN*************** (7)(MUST)
0305	Number of Islands II	Java	O(k a(m * n))*	O(m n)*	Hard	graph, union find, LC 200, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN (1)
0323	Number of Connected Components in an Undirected Graph	Python , Java	O(n + e)	O(n)	Medium	graph, LC 547, 🔒, bfs, dfs, Union Find, `linkedin`, `amazon`, `fb`, `google`, `microsoft`, `apple`, `blind75`	AGAIN************** (6) (MUST)
0778	Swim in Rising Water	Java	O(n^2 logn)*	O(n^2)	Medium	graph, Dijkstra, `google`, `amazon`, `fb`, `neetcode150`	AGAIN1 (1) (not start)
0959	Regions Cut By Slashes	Python, Java	O(n^2 a(n^2))*	O(n^2)	Medium	graph, Union Find, `amazon`, `apple`, `uber`	again
0997	Find the Town Judge	Python, Java	O(n + e)	O(n)	Easy	graph, in-degree minus out-degree equals n - 1, `good basic`, `google`, `amazon`, `apple`, `neetcode250`	again
1135	Connecting Cities With Minimum Cost	Python, Java	O(e loge)*	O(n)	Medium	graph, union find, Kruskal, prime, `amazon`, `google`, `uber`	AGAIN (not start)
1462	Course Schedule IV	Java	O(n^3)	O(n^2)	Medium	graph, Floyd-Warshall reachability, or topological sort with reach sets, LC 207, `amazon`, `uber`, `neetcode250`	AGAIN (not start)
1489	Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree	Java	O(e^2 a(n))*	O(n + e)	Hard	graph, dfs, bfs, Dijkstra, `amazon`, `neetcode250`	AGAIN (not start)
1514	Path with Maximum Probability	Python, Java	O(e logn)*	O(n + e)	Medium	graph, Dijkstra, `google`	AGAIN (not start)
1584	Min Cost to Connect All Points	Java	O(n^2 logn)*	O(n^2)	Medium	graph, Kruskal algo, Prim algo, advanced graph, `amazon`, `neetcode150`	AGAIN (not start)
1631	Path With Minimum Effort	Python, Java	O(m nlog(m * n))*	O(m n)*	Medium	graph, `Max of step differences`, dfs, bfs+PQ, LC 64, Dijkstra, `google`, `amazon`, `neetcode250`	AGAIN********** (2)(MUST)
1761	Minimum Degree of a Connected Trio in a Graph	Java	O(n^3)	O(n^2)	Hard	graph, DP, `amazon`	AGAIN (not start)
1971	Find if Path Exists in Graph	Java	O(n + e)	O(n + e)	Easy	graph, bfs, dfs, union find, `google`, `amazon`, `microsoft`	AGAIN (1)
2290	Minimum Obstacle Removal to Reach Corner	Java	O(m nlog(m * n))*	O(m n)*	Hard	graph, bfs, PQ, Dijkstra classics	AGAIN****** (2)(MUST)
2392	Build a Matrix With Conditions	Java	O(k^2)	O(k^2)	Hard	graph, dfs, bfs, Dijkstra, `neetcode250`	AGAIN (not start)
2508	Add Edges to Make Degrees of All Nodes Even	Java	O(n + e)	O(n + e)	Hard	graph, LC weekly	AGAIN (not start)
2617	Minimum Number of Visited Cells in a Grid	Java	O(m nlog(m * n))*	O(m n)*	Hard	graph, PQ, stack, LC weekly	AGAIN***** (1) (not start)
2642	Design Graph With Shortest Path Calculator	Java	ctor: O(n^3), addEdge: O(n^2), shortestPath: O(1)	O(n^2)	Medium	graph, Dijkstra, floyd warshall, LC weekly 102	AGAIN******** (2)
2709	Greatest Common Divisor Traversal	Java	O(n sqrt(maxV) * a(n))*	O(n + maxV)	Hard	graph, union find over shared prime factors, sieve, `complex`, `neetcode250`	AGAIN (not start)
3123	Find Edges in Shortest Paths	Java	O(e logn)*	O(n + e)	Hard	graph, Dijkstra from both ends, keep edges lying on some shortest path, `good trick`	AGAIN (1) (not start)

Geometry

#	Title	Solution	Time	Space	Difficulty	Note	Status
0587	Erect the Fence	Python, Java	O(nlogn)	O(n)	Hard	geometry, complex, Convex Hull, `Monotone Chain`, `amazon`, `google`	AGAIN (not start)
0892	Surface Area of 3D Shapes	Java	O(n^2)	O(1)	Easy	geometry, count 6 faces per cube then subtract hidden overlaps, `matrix`, `math`, `amazon`	AGAIN

Design

#	Title	Solution	Time	Space	Difficulty	Note	Status
0146	LRU Cache	Python, Java	O(1)	O(k)	Medium	design, good basic, LRU, dequeue, `Double Linkedlist`, LinkedHashMap, OrderedDict, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode150`, `top100liked`, `netflix`	AGAIN********** (5)
0225	Implement Stack using Queues	Python, Java	push: O(n), pop: O(1), top: O(1)	O(n)	Easy	design, two queues, or one queue rotated after each push, LC 232, `basic`, `amazon`, `microsoft`, `neetcode250`	AGAIN** (1)(MUST)
0284	Peeking Iterator	C++ Python, Java	O(1)	O(1)	Medium	design, good basic, `google`, `apple`, `amazon`, `fb`, `microsoft`	not start*** (1)
0348	Design Tic-Tac-Toe	Python, Java	O(1)	O(n^2)	Medium	design, matrix, array, 🔒, `google`, `fb`, `amazon`, `apple`, `microsoft`, `uber`	AGAIN****** (5)
0353	Design Snake Game	Python, Java	O(1)	O(s)	Medium	design, good trick, Deque, 🔒, `amazon`, `google`, `square`, `microsoft`, `fb`, `apple`, `uber`	AGAIN*** (1)
0355	Design Twitter	Python, Java	O(klogu)	O(t + f)	Medium	design, good trick, data structure, heapq, defaultdict, `amazon`, `apple`, `microsoft`, `neetcode150`	OK******** (6)
0362	Design Hit Counter	Java	O(1), amortized	O(k)	Medium	design, 🔒, deque, sliding window count, `google`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	Again (1)
0379	Design Phone Directory	Java	O(1)	O(n)	Medium	design, 🔒, queue, free-slot pool, `google`, `amazon`	AGAIN(1)
0380	Insert Delete GetRandom O(1)	Python, Java	O(1)	O(n)	Medium	design, set, list, dict, `amazon`, `fb`, `google`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	OK* (5)
0381	Insert Delete GetRandom O(1) - Duplicates allowed	C++ Python, Java	O(1) average	O(n)	Hard	design, LC 380, hashmap of value -> index set + swap-with-last, `good trick`, `google`, `amazon`, `fb`, `apple`, `uber`, `linkedin`
0432	All O`one Data Structure	Java	O(1) per op	O(n)	Hard	design, doubly linked list of count buckets + hashmap, LC 146, LC 460, `complex`, `google`, `amazon`, `fb`, `uber`, `linkedin`
0460	LFU Cache	Python, Java	O(1)	O(k)	Hard	design, Least Frequently Used (LFU) cache, complex, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`, `neetcode250`	AGAIN*** (3)
0535	Encode and Decode TinyURL	Python, Java	O(1)	O(n)	Medium	design, `hash map`, “duplicated”, “hash map collision”, `uber`, `amazon`, `google`, `fb`, `microsoft`	OK**** (5)
0588	Design In-Memory File System	Python, Java	ls: O(l + klogk) mkdir: O(l) addContentToFile: O(l + c) readContentFromFile: O(l + c)	O(n + s)	Hard	design, dict, a bit complex basic, 🔒, shoptify, `amazon`, `google`, `microsoft`, `uber`	AGAIN******* (3)
0604	Design Compressed String Iterator	C++ Python, Java	ctor: O(n), next/hasNext: O(1)	O(n)	Easy	design, 🔒, decode (char, count) pairs lazily, iterator, `google`
0631	Design Excel Sum Formula	C++ Python, Java	set: O(1) get: O((r c)^2)* sum: O((r c)^2)*	O(r c)*	Hard	design, 🔒, `google`, `amazon`, `microsoft`, `uber`
0635	Design Log Storage System	C++ Python, Java	put: O(1) retrieve: O(n + dlogd)	O(n)	Medium	design, 🔒, `google`, `amazon`
0641	Design Circular Deque	Python, Java	O(1) per op	O(k)	Medium	design, 🔒, circular buffer or doubly linked list, LC 622, `amazon`, `fb`
0642	Design Search Autocomplete System	Python, Java	O(p^2)	O(p t + s)*	Hard	design, 🔒, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`	AGAIN**** (not start) (5)
0705	Design HashSet	Java	O(1) average	O(n)	Easy	design, bucket array + chaining, LC 706, `good basic`, `google`, `microsoft`, `neetcode250`
0706	Design HashMap	Java	O(1) average	O(n)	Easy	design, bucket array + chaining, LC 705, `good basic`, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `neetcode250`
0715	Range Module	C++ Python, Java	add: O(n) remove: O(n) query: O(logn)	O(n)	Hard	design, sorted interval list with binary search, LC 352, TreeMap, segment tree, `google`, `amazon`, `fb`, `linkedin`
0716	Max Stack	Python, Java	push: O(logn) pop: O(logn) popMax: O(logn) top: O(1) peekMax: O(1)	O(n)	Hard	design, basic, stack, `amazon`, `google`, `fb`, `apple`, `microsoft`, `uber`, `linkedin`, `bloomberg`	again*
0745	Prefix and Suffix Search	Python, Java	ctor: O(w l^2)* search : O(p + s)	O(t)	Hard	design, Trie, `fb`, `google`	Not start* (1) (good basic)
0900	RLE Iterator	C++ Python, Java	O(n)	O(1)	Medium	design, `google`, treemap, array, `amazon`	AGAIN (not start) (1)
1146	Snapshot Array	Java	set: O(1) get: O(logn)	O(n)	Medium	design, treeMap, binary search, `google`, `amazon`, `fb`, `apple`, `microsoft`, `uber`	AGAIN*** (1)
1166	Design File System	C++ Python, Java	create: O(n) get: O(n)	O(n)	Medium	design, 🔒, `google`, `airbnb`, `amazon`, `microsoft`	AGAIN***** (1)
1172	Dinner Plate Stacks	C++ Python, Java	push: O(logn) pop: O(1), amortized popAtStack: (logn)	O(n c)*	Hard	design, PQ of indices of non-full stacks, `good trick`
1188	Design Bounded Blocking Queue	Java	O(1) per op	O(k)	Medium	design, `google`, Semaphore, `concurrency`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`	AGAIN (not start)
1206	Design Skiplist	C++ Python, Java	O(logn), on average	O(n)	Hard	design, probabilistic multi-level linked list, `complex`, `google`, `fb`, `microsoft`
1236	Web Crawler	C++ Python	O(V + E)	O(V)	Medium	design, 🔒, BFS, DFS, `string`, `google`, `amazon`, `fb`, `microsoft`
1244	Design A Leaderboard	Python, Java	ctor: O(1) add: O(1) top: O(n) reset: O(1)	O(n)	Medium	design, `google`, hashmap, `amazon`, `fb`, `uber`	AGAIN (not start)
1268	Search Suggestions System	Python, Java	ctor: O(n l)* suggest: O(l^2)	O(t)	Medium	design, good basic, array, heap, sort, Trie, `amazon`, `string`, `binary search`, `google`, `apple`, `microsoft`	AGAIN******** (3)
1286	Iterator for Combination	Python	ctor: O(1), next: O(k)	O(k)	Medium	design, Stack, `google`, `uber`
1381	Design a Stack With Increment Operation	Java	O(1) per op	O(n)	Medium	design, array, stack, lazy increment (`good trick`), linked list, `google`, `amazon`	AGAIN (1)
1429	First Unique Number	Python, Java	O(1) amortized per op	O(n)	Medium	design, good trick, heap, `amazon`, `fb`	AGAIN*** (not start)
1472	Design Browser History	Python, Java	visit: O(1), back/forward: O(steps)	O(n)	Medium	design, two stacks, or a list with a cursor, `good basic`, `google`, `amazon`, `microsoft`	AGAIN
1500	Design a File Sharing System	Python, Java	join/leave: O(logn), request: O(n)	O(n)	Medium	design, 🔒, min-heap of free ids + hashmap of owners, `google`	AGAIN*** (not start)
1603	Design Parking System	Python, Java	O(1)	O(1)	Easy	design, `amazon`, `paypal`, `google`, `microsoft`	OK
1628	Design an Expression Tree With Evaluate Function	Python, Java	build: O(n), evaluate: O(n)	O(n)	Medium	design, complex, `amazon`	AGAIN*** (not start)
1656	Design an Ordered Stream	Python, Java	insert: O(1) amortized	O(n)	Easy	design, pointer + bucket array, return the contiguous chunk, `basic`
1670	Design Front Middle Back Queue	Python, Java	O(1) per op	O(n)	Medium	design, good basic, `amazon`	AGAIN** (1) (not start)
1756	Design Recent Used Queue	Python, Java	fetch: O(k)	O(n)	Medium	design, 🔒, move-to-front list or BIT, LC 146, `google`	AGAIN
1797	Design Authentication Manager	Python, Java	O(1) amortized	O(n)	Medium	design, hashmap	AGAIN
1976	Number of Ways to Arrive at Destination	Python, Java	O(e logn)*	O(n + e)	Medium	design, Dijkstra + count shortest paths, dp, mod 1e9+7, `graph`, `topological sort`, `fb`
2034	Stock Price Fluctuation	Python, Java	update: O(logn) current: O(1) maximum/minimum: O(logn) amortized	O(n)	Medium	design, hashmap is the source of truth + two lazy heaps, pop stale tops instead of deleting, heap, `good trick`, LC weekly	AGAIN(1)

Prefix Sum

#	Title	Solution	Time	Space	Difficulty	Note	Status
1124	Longest Well-Performing Interval	Python, Java	O(n)	O(n)	Medium	prefix sum, hashmap, first idx, Monotonic Stack, good basic, `google`	AGAIN************* (3)(MUST)
2012	Sum of Beauty in the Array	Python	O(n)	O(n)	Medium	prefix sum, good basics, prefix, suffix sum, LC weekly	AGAIN****** (2)
2017	Grid Game	Python	O(n)	O(1)	Medium	prefix sum, 2 x n grid, path == turning column, prefix (bottom) + suffix (top) sum, minimax, greedy, LC weekly	AGAIN(1)

Simulation

#	Title	Solution	Time	Space	Difficulty	Note	Status
0874	Walking Robot Simulation	C++ Python	O(n + k)	O(k)	Easy	simulation, hashset of obstacles, direction array, LC 1041, `good basic`, `amazon`

Concurrency

#	Title	Solution	Time	Space	Difficulty	Note
1114	Print in Order	C++ Python	O(n)	O(1)	Easy	concurrency, two semaphores (or CountDownLatch), enforce sequential ordering, `google`, `amazon`, `apple`, `microsoft`, `bloomberg`
1115	Print FooBar Alternately	C++ Python	O(n)	O(1)	Medium	concurrency, two semaphores alternating foo/bar
1116	Print Zero Even Odd	C++ Python	O(n)	O(1)	Medium	concurrency, three semaphores: zero releases even or odd
1117	Building H2O	C++ Python	O(n)	O(1)	Hard	concurrency, two semaphores sized 2 (H) and 1 (O), barrier per molecule, `linkedin`
1188	Design Bounded Blocking Queue	C++ Python	O(1) per op	O(k)	Medium	concurrency, 🔒, BlockingQueue with a Condition, or two counting semaphores, producer-consumer, `google`, `amazon`, `apple`, `microsoft`, `uber`, `linkedin`
1195	Fizz Buzz Multithreaded	C++ Python	O(n)	O(1)	Medium	concurrency, four semaphores, one per printer, LC 412, `apple`, `microsoft`
1226	The Dining Philosophers	C++ Python	O(n)	O(1)	Medium	concurrency, resource ordering, or allow at most 4 diners, deadlock avoidance, `google`, `apple`
1242	Web Crawler Multithreaded	C++ Python	O(\|V\| + \|E\|)	O(\|V\|)	Medium	concurrency, 🔒, BFS, DFS, thread pool, `fb`, `microsoft`
1279	Traffic Light Controlled Intersection	C++ Python	O(n)	O(1)	Easy	concurrency, 🔒, single lock guarding the shared green-light state

SQL

#	Title	Solution	Time	Space	Difficulty	Note	Status
0175	Combine Two Tables	MySQL	O(m + n)	O(m + n)	Easy	sql, left join on two tables, `good basic`, `google`, `amazon`, `fb`, `apple`	OK (4)
0176	Second Highest Salary	MySQL	O(n)	O(1)	Easy	sql, `amazon`, `fb`, `google`, `apple`, `microsoft`	OK (4)
0177	Nth Highest Salary	MySQL	O(n^2)	O(n)	Medium	sql, `MySQL PROCEDURE`, `SQL FAQ`, `google`, `amazon`, `fb`, `apple`, `uber`	AGAIN*** (3)
0178	Rank Scores	MySQL	O(n^2)	O(n)	Medium	sql, `trick`, `SQL var`, ank, select same table, rank, `amazon`, `fb`, `apple`	AGAIN****** (7)
0180	Consecutive Numbers	MySQL	O(n)	O(n)	Medium	sql, `SQL var`, join same table multi times, `amazon`	OK* (3)
0181	Employees Earning More Than Their Managers	MySQL	O(n^2)	O(1)	Easy	sql, self join on manager id, `good basic`, `google`, `amazon`, `fb`, `apple`	OK
0182	Duplicate Emails	MySQL	O(n^2)	O(n)	Easy	sql, group by + having count > 1, `good basic`	OK
0183	Customers Who Never Order	MySQL	O(n^2)	O(1)	Easy	sql, left join, `amazon`	OK** (3) (but again)
0184	Department Highest Salary	MySQL	O(n^2)	O(n)	Medium	sql, `trick`, where, good basic, `amazon`, `fb`, `apple`, `microsoft`	OK***** (but again) (6)
0185	Department Top Three Salaries	MySQL	O(n^2)	O(n)	Hard	sql, similiar as `# 0177 Nth Highest Salary`, good trick, top N in group, `google`, `amazon`, `uber`, `netflix`	AGAIN******** (5)
0196	Delete Duplicate Emails	MySQL	O(n^2)	O(n)	Easy	sql, DELETE with self join, good basic, `SQL FAQ`, `amazon`, `fb`	AGAIN (2)
0197	Rising Temperature	MySQL	O(n^2)	O(n)	Easy	sql, self join on date - 1, or LAG window function, `amazon`	OK
0262	Trips and Users	MySQL	O((t u) + tlogt)*	O(t)	Hard	sql, case condisions, `amazon`, `fb`, `uber`	OK* (2)
0511	Game Play Analysis I	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK
0512	Game Play Analysis II	MySQL	O(n)	O(n)	Easy	sql, 🔒, `2 col where` `good trick`	AGAIN**(4)
0534	Game Play Analysis III	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, `SQL var`, `tricky`, window func	AGAIN******** (6)
0550	Game Play Analysis IV	MySQL	O(n)	O(n)	Medium	sql, case, fraction, join, good basic, where min condition	OK*********** (7) (but again)
0569	Median Employee Salary	MySQL	O(n)	O(n)	Medium	sql, medium number, `google`	AGAIN* (not start)
0571	Find Median Given Frequency of Numbers	MySQL	O(n)	O(n)	Medium	sql, medium number	AGAIN** (not start) (2)
0577	Employee Bonus	MySQL	O(n)	O(n)	Easy	sql, left join + where is null or condition, `good basic`	OK
0578	Get Highest Answer Rate Question	MySQL	O(m + n)	O(n)	Medium	sql, `fb`, case condition	OK* (3)
0579	Find Cumulative Salary of an Employee	MySQL	O(n^2)	O(n)	Hard	sql, window function, `amazon`, good trick	OK***** (5)(but again)
0580	Count Student Number in Departments	MySQL	O(m + n)	O(n)	Medium	sql, 🔒, left join + group by, count students per department	OK*** (2) (but again)
0595	Big Countries	MySQL	O(n)	O(n)	Easy	sql, simple where with an OR condition, `basic`, `google`, `bloomberg`	OK
0597	Friend Requests I: Overall Acceptance Rate	MySQL	O(n)	O(n)	Medium	sql, select distinct, ifnull, `fb`	OK*** (7)
0601	Human Traffic of Stadium	MySQL	O(n)	O(n)	Hard	sql, consecutive nums, `amazon`	OK* (1)
0602	Friend Requests II: Who Has Most Friend?	MySQL	O(n)	O(n)	Medium	sql, union all, `fb`, `amazon`	OK*** (4)
0603	Consecutive Available Seats	MySQL	O(n^2)	O(n)	Medium	sql, consecutive nums, good basic, cross join, `amazon`	OK***** (3)(but again)
0618	Students Report By Geography	MySQL	O(nlogn)	O(n)	Hard	sql, sql var, `amazon`	AGAIN (not start)
0620	Not Boring Movies	MySQL	O(n)	O(n)	Easy	sql, simple where + order by, `basic`	OK
0626	Exchange Seats	MySQL	O(n)	O(n)	Medium	sql, CASE on id parity, count total rows, good trick, `amazon`	AGAIN (not start)
0627	Swap Salary	MySQL	O(n)	O(n)	Easy	sql, UPDATE with CASE, good basic, `amazon`	OK* (1) (but again)
1045	Customers Who Bought All Products	MySQL	O(n + k)	O(n + k)	Medium	sql, 🔒, where with count, `amazon`	OK*** (4)
1050	Actors and Directors Who Cooperated At Least Three Times	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK
1068	Product Sales Analysis I	MySQL	O(m + n)	O(m + n)	Easy	sql, 🔒, `amazon`	OK
1069	Product Sales Analysis II	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK
1070	Product Sales Analysis III	MySQL	O(n)	O(n)	Medium	sql, 🔒, `amazon`	OK
1075	Project Employees I	MySQL	O(m + n)	O(m + n)	Easy	sql, 🔒, `fb`	OK
1076	Project Employees II	MySQL	O(n)	O(n)	Easy	sql, 🔒, `fb`	OK (2)
1077	Project Employees III	MySQL	O((m + n)^2)	O(m + n)	Medium	sql, 🔒, `tricky where`, `fb`	OK***** (2) (but again)
1082	Sales Analysis I	MySQL	O(n)	O(n)	Easy	sql, 🔒, group by only 1 col, good basic, `amazon`	OK***** (5) (again)
1083	Sales Analysis II	MySQL	O(m + n)	O(m + n)	Easy	sql, 🔒, not in, `amazon`	OK*** (3) (again)
1084	Sales Analysis III	MySQL	O(m + n)	O(m + n)	Easy	sql, 🔒, `amazon`	OK** (2)
1097	Game Play Analysis V	MySQL	O(n^2)	O(n)	Hard	sql, 🔒, `good basic`, `retention`, case condition, data_add, left join	AGAIN******* (8)
1098	Unpopular Books	MySQL	O(m + n)	O(n)	Medium	sql, 🔒, where not in, `amazon`	OK* (2)
1107	New Users Daily Count	MySQL	O(n)	O(n)	Medium	sql, 🔒, `amazon`, `linkedin`	OK*
1112	Highest Grade For Each Student	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, good basic	OK** (4)
1113	Reported Posts	MySQL	O(n)	O(n)	Easy	sql, 🔒, `fb`	OK
1126	Active Businesses	MySQL	O(n)	O(n)	Medium	sql, 🔒, `good basic`	AGAIN*** (3)
1127	User Purchase Platform	MySQL	O(n)	O(n)	Hard	sql, 🔒, `complex`, union all, case, `linkedin`	OK**** (6) (but again)
1132	Reported Posts II	MySQL	O(m + n)	O(n)	Medium	sql, 🔒, `fb`	OK*** (4)
1141	User Activity for the Past 30 Days I	MySQL	O(n)	O(n)	Easy	sql, 🔒, `fb`	AGAIN* (2)
1142	User Activity for the Past 30 Days II	MySQL	O(n)	O(n)	Easy	sql, 🔒, `fb`	AGAIN* (1)
1148	Article Views I	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, `linkedin`	OK
1149	Article Views II	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, `amazon`, `linkedin`	OK*
1158	Market Analysis I	MySQL	O(m + n)	O(m + n)	Medium	sql, 🔒, `case when ... is not null`	AGAIN**** (5)
1159	Market Analysis II	MySQL	O(m + n)	O(m + n)	Hard	sql, 🔒, good trick	AGAIN** (3)
1164	Product Price at a Given Date	MySQL	O(mlogn)	O(m)	Medium	sql, 🔒, good trick, union, case, not in a period, `amazon`	AGAIN******** (2)
1173	Immediate Food Delivery I	MySQL	O(n)	O(1)	Easy	sql, 🔒	OK
1174	Immediate Food Delivery II	MySQL	O(n)	O(m)	Medium	sql, 🔒	OK**** (3)
1179	Reformat Department Table	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`, `apple`	OK
1193	Monthly Transactions I	MySQL	O(n)	O(n)	Medium	sql, 🔒	OK (2)
1194	Tournament Winners	MySQL	O(m + n + nlogn)	O(m + n)	Hard	sql, 🔒	AGAIN*
1204	Last Person to Fit in the Elevator	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, cumsum, window func, good basic	OK****** (3)
1205	Monthly Transactions II	MySQL	O(n)	O(n)	Medium	sql, 🔒, good trick, union all, case conditions	OK*** (3) (but again)
1211	Queries Quality and Percentage	MySQL	O(n)	O(n)	Easy	sql, avg with CASE, round, `good basic`, `fb`	OK
1212	Team Scores in Football Tournament	MySQL	O(nlogn)	O(n)	Medium	sql, good trick	OK** (2)
1225	Report Contiguous Dates	MySQL	O(nlogn)	O(n)	Hard	sql, 🔒, `amazon`, `fb`	AGAIN* (2) (not start)
1241	Number of Comments per Post	MySQL	O(n)	O(n)	Easy	sql, 🔒, good basic, `fb`	OK**** (5) (but again)
1251	Average Selling Price	MySQL	O(n)	O(n)	Easy	sql, 🔒, good basic, `amazon`	OK*** (but again) (3)
1264	Page Recommendations	MySQL	O(m + n)	O(m)	Medium	sql, 🔒, `fb`	OK** (2)
1270	All People Report to the Given Manager	MySQL	O(n)	O(n)	Medium	sql, 🔒, good basic, `google`, `amazon`	OK* (3)
1280	Students and Examinations	MySQL	O((m n) * log(m * n))*	O(m n)*	Easy	sql, 🔒	OK (1)
1285	Find the Start and End Number of Continuous Ranges	MySQL	O(n)	O(n)	Medium	sql, 🔒, variable, `amazon`	AGAIN (not start) (1)
1294	Weather Type in Each Country	MySQL	O(m + n)	O(n)	Easy	sql, 🔒	OK (1)
1303	Find the Team Size	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	ok (1)
1308	Running Total for Different Genders	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, good basic, union all, window func	OK**** (3)
1321	Restaurant Growth	MySQL	O(n^2)	O(n)	Medium	sql, 🔒, good basic, trick, `amazon`	AGAIN***** (3)
1322	Ads Performance	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, good basic, `fb`	OK******* (3) (but again)
1327	List the Products Ordered in a Period	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK
1336	Number of Transactions per Visit	MySQL	O(m + n)	O(m + n)	Medium	sql, 🔒, complex, variable	AGAIN (not start)
1341	Movie Rating	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒	AGAIN (not start)
1350	Students With Invalid Departments	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK
1355	Activity Participants	MySQL	O(n)	O(n)	Medium	sql, 🔒	OK
1364	Number of Trusted Contacts of a Customer	MySQL	O(n + m + l + nlogn)	O(n + m + l)	Medium	sql, 🔒	OK
1369	Get the Second Most Recent Activity	MySQL	O(nlogn)	O(n)	Hard	sql, 🔒, union, having	OK** (2) (but again)
1378	Replace Employee ID With The Unique Identifier	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1384	Total Sales Amount by Year	MySQL	O(nlogn)	O(n)	Hard	sql, 🔒, complex	OK*
1393	Capital Gain/Loss	MySQL	O(n)	O(n)	Medium	sql, 🔒	OK
1398	Customers Who Bought Products A and B but Not C	MySQL	O(m + n)	O(m + n)	Medium	sql, 🔒, `amazon`, `fb`	OK
1407	Top Travellers	MySQL	O(m + nlogn)	O(m + n)	Easy	sql, 🔒, ifnull	OK*
1412	Find the Quiet Students in All Exams	MySQL	O(m + nlogn)	O(m + n)	Hard	sql, 🔒, good trick, not in, inner join on multiple cols	OK**** (3) (but again)
1421	NPV Queries	MySQL	O(n)	O(n)	Medium	sql, 🔒, `amazon`	OK
1435	Create a Session Bar Chart	MySQL	O(n)	O(1)	Easy	sql, 🔒	OK
1440	Evaluate Boolean Expression	MySQL	O(n)	O(n)	Medium	sql, 🔒	OK
1445	Apples & Oranges	MySQL	O(n)	O(n)	Medium	sql, 🔒, `fb`	OK
1454	Active Users	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, good basic, window func, `amazon`	AGAIN*** (2)
1459	Rectangles Area	MySQL	O(n^2)	O(n^2)	Medium	sql, 🔒	OK*
1468	Calculate Salaries	MySQL	O(m + n)	O(m + n)	Easy	sql, 🔒	OK*
1479	Sales by Day of the Week	MySQL	O(m + n)	O(n)	Hard	sql, 🔒, case, DAYOFWEEK, `amazon`	OK
1484	Group Sold Products By The Date	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, `GROUP_CONCAT`	OK*
1495	Friendly Movies Streamed Last Month	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK
1501	Countries You Can Safely Invest In	MySQL	O(n)	O(n)	Medium	sql, 🔒, good trick, group avg, global avg, SUBSTRING, inner join on `or conditions`	OK****** (4)
1511	Customer Order Frequency	MySQL	O(n)	O(n)	Easy	sql, 🔒, having, like, `amazon`, `fb`	OK* (1)
1517	Find Users With Valid E-Mails	MySQL	O(n)	O(n)	Easy	sql, 🔒, regular expression, `apple`	AGAIN
1527	Patients With a Condition	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1532	The Most Recent Three Orders	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, window func, good basic	OK** (2) (but again)
1543	Fix Product Name Format	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, trim	OK
1549	The Most Recent Orders for Each Product	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, max day per id, good basic	OK* (again)
1555	Bank Account Summary	MySQL	O(m + n)	O(m + n)	Medium	sql, 🔒, union all, good trick	OK**** (2)(but again)
1565	Unique Orders and Customers Per Month	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1571	Warehouse Manager	MySQL	O(n)	O(n)	Medium	sql, 🔒, `amazon`	OK* (1)
1581	Customer Who Visited but Did Not Make Any Transactions	MySQL	O(n)	O(n)	Easy	sql, 🔒, left join, good basic	OK** (2)(but again)
1587	Bank Account Summary II	MySQL	O(m + n)	O(m + n)	Easy	sql, 🔒	OK
1596	The Most Frequently Ordered Products for Each Customer	MySQL	O(n)	O(n)	Medium	sql, 🔒, good trick, `rank() ORDER BY count`, get max in each group, `amazon`	OK********* (3)(but again)
1607	Sellers With No Sales	MySQL	O(nlogm)	O(n + m)	Medium	sql, 🔒	OK
1613	Find the Missing IDs	MySQL	O(n^2)	O(n)	Medium	sql, 🔒, `RECURSIVE CTE`, good trick, `amazon`	AGAIN*** (2)
1623	All Valid Triplets That Can Represent a Country	MySQL	O(n^3)	O(n^3)	Easy	sql, 🔒, `<>`, `amazon`	AGAIN* (not start)
1633	Percentage of Users Attended a Contest	MySQL	O(m + nlogn)	O(n)	Easy	sql, 🔒	OK
1635	Hopper Company Queries I	MySQL	O(d + r + tlogt)	O(d + r + t)	Hard	sql, 🔒, complex, `uber`	AGAIN (not start)
1645	Hopper Company Queries II	MySQL	O(d + r + tlogt)	O(d + r + t)	Hard	sql, 🔒, complex, `uber`	AGAIN (not start)
1651	Hopper Company Queries III	MySQL	O(d + r + tlogt)	O(d + r + t)	Hard	sql, 🔒, complex, `uber`	AGAIN (not start)
1661	Average Time of Process per Machine	MySQL	O(n)	O(n)	Easy	sql, 🔒, good basic, `amazon`, `fb`	OK* (1)
1667	Fix Names in a Table	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, concat, sub-string	OK (1)
1677	Product’s Worth Over Invoices	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒	OK
1683	Invalid Tweets	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1693	Daily Leads and Partners	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1699	Number of Calls Between Two Persons	MySQL	O(n)	O(n)	Medium	sql, 🔒, cte, union all, `amazon`, `fb`	OK* (1)(but again)
1709	Biggest Window Between Visits	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, window func, datediff, coalesce, good trick	AGAIN***** (2)
1715	Count Apples and Oranges	MySQL	O(n)	O(n)	Medium	sql, 🔒, ifnull	OK (2)
1729	Find Followers Count	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒	OK
1731	The Number of Employees Which Report to Each Employee	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒	OK
1741	Find Total Time Spent by Each Employee	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, `amazon`	OK
1747	Leetflex Banned Accounts	MySQL	O(n^2)	O(n)	Medium	sql, 🔒	OK (2) (but again)
1757	Recyclable and Low Fat Products	MySQL	O(n)	O(n)	Easy	sql, 🔒, `fb`	OK
1767	Find the Subtasks That Did Not Execute	MySQL	O(n c)*	O(n c)*	Hard	sql, 🔒, `RECURSIVE CTE`, `google`	AGAIN (not start)
1777	Product’s Price for Each Store	MySQL	O(n)	O(n)	Easy	sql, 🔒, `amazon`	OK (2)
1783	Grand Slam Titles	MySQL	O(n)	O(n)	Medium	sql, 🔒, union all, good basic, `amazon`	OK* (1) (but again)
1789	Primary Department for Each Employee	MySQL	O(n)	O(n)	Easy	sql, 🔒, where id in	OK (1) (but again)
1795	Rearrange Products Table	MySQL	O(n)	O(n)	Easy	sql, 🔒, union all, good basic, `amazon`	OK****** (2)
1809	Ad-Free Sessions	MySQL	O(n)	O(n)	Easy	sql, 🔒, left join where col is null, `amazon`	OK**** (3)(but again)
1811	Find Interview Candidates	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, union all, cte, where, `good basic`, `amazon`	AGAIN* (2)
1821	Find Customers With Positive Revenue this Year	MySQL	O(n)	O(n)	Easy	sql, 🔒, `google`	OK
1831	Maximum Transaction Each Day	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, rank(), where on 2 attr, good basic	AGAIN**** (2)
1841	League Statistics	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, case, complex	AGAIN* (2)
1843	Suspicious Bank Accounts	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, good trick, window func	OK** (2) (but AGAIN)
1853	Convert Date Format	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1867	Orders With Maximum Quantity Above Average	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK (1)
1873	Calculate Special Bonus	MySQL	O(n)	O(n)	Easy	sql, 🔒, left, odd num	OK (2)
1875	Group Employees of the Same Salary	MySQL	O(nlogn)	O(n)	Medium	sql, 🔒, complex, good basic	AGAIN* (1)
1890	The Latest Login in 2020	MySQL	O(n)	O(n)	Easy	sql, 🔒	OK
1892	Page Recommendations II	MySQL	O(n m)*	O(n m)*	Hard	sql, 🔒, join on friendship + page likes, `not in`, `fb`	AGAIN*** (1) (not start)
1907	Count Salary Categories	MySQL	O(n)	O(n)	Medium	sql, 🔒, union all	OK* (1)
1917	Leetcodify Friends Recommendations	MySQL	O(n^2)	O(n^2)	Hard	sql, 🔒, `NOT EXISTS`	AGAIN*** (2)
1919	Leetcodify Similar Friends	MySQL	O(n l)*	O(n l)*	Hard	sql, 🔒	AGAIN* (not start)
1934	Confirmation Rate	MySQL	O(n + m)	O(n + m)	Medium	sql, 🔒, good basic	OK* (1) (but again)
1939	Users That Actively Request Confirmation Messages	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, TIMESTAMPDIFF, good basic	OK*** (2) (but again)
1949	Strong Friendship	MySQL	O(n^3)	O(n^2)	Medium	sql, 🔒, good basic, self join, where on 2 cols, `fb`	OK* (2) (but again)
1951	All the Pairs With the Maximum Number of Common Followers	MySQL	O(n^3)	O(n^2)	Medium	sql, 🔒, good trick	AGAIN* (2)
1965	Employees With Missing Information	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒, good basic	OK* (1) (but again)
1972	First and Last Call On the Same Day	MySQL	O(n)	O(n)	Hard	sql, 🔒, rank, union all, `amazon`	AGAIN** (2)
1978	Employees Whose Manager Left the Company	MySQL	O(nlogn)	O(n)	Easy	sql, 🔒	OK (1)
1988	Find Cutoff Score for Each School	MySQL	O(n m)*	O(n m)*	Medium	sql, 🔒, no ref	AGAIN (not start)
1990	Count the Number of Experiments	MySQL	O(n)	O(n)	Easy	sql, 🔒, cross join	AGAIN* (1)
2004	The Number of Seniors and Juniors to Join the Company	MySQL	O(nlogn)	O(n)	Hard	sql, 🔒, not ref	AGAIN (not start)

Shell Script

#	Title	Solution	Time	Space	Difficulty	Note
0192	Word Frequency	Shell	O(n)	O(k)	Medium	shell, awk word count then sort by frequency, `good basic`, `google`, `amazon`, `fb`, `apple`
0193	Valid Phone Numbers	Shell	O(n)	O(1)	Easy	shell, grep with a regular expression, `basic`, `amazon`, `apple`, `uber`
0194	Transpose File	Shell	O(n^2)	O(n^2)	Medium	shell, awk transpose with a 2D array, `good trick`
0195	Tenth Line	Shell	O(n)	O(1)	Easy	shell, sed / awk NR == 10, `basic`, `google`, `apple`

Newly Added (kamyu104 gap)

Problems imported from the coverage audit against kamyu104/LeetCode-Solutions.

These solutions were generated from the problem statements and have not been run against LeetCode’s judge. Treat them as drafts to review, not as verified-accepted answers.

Ranges covered so far: 0001-1000 (127 problems) and 1001-3687 (1855 problems) — 1982 in total.