Multi-Source BFS

Enqueue all sources at once; spread like ripples. LC 994 (Rotting Oranges), 542 (01 Matrix), 1162.

Source (rotten)

Fresh (target)

Spreading

Rotted (step label)

Blocked

Grid size Sources (rotten): 3 Speed

Time: O(V+E) | All sources enqueued at t=0