Rotting Oranges

Each minute, rot spreads to adjacent fresh oranges; return the minutes until none remain fresh.

BFS → · High frequency · Solve on LeetCode →

Try it

Step through the core mechanic. The simulator below runs the bfs shape this problem is built on.

Interactive · grid flood-fill

◦

queue (front → back)

(0,0)

seed the queue with the start cell (0,0)

step 1 / 5

BFS vs DFS, same grid. Swap the frontier from a queue to a stack and breadth-first becomes depth-first. Both visit exactly the same cells; only the order differs. BFS layers outward (shortest-path / wave problems); DFS plunges down one branch (component / path problems).

The approach

Seed a queue with every rotten orange at once (multi-source BFS). Each BFS layer is one minute; the answer is the layer count. If fresh oranges survive, return −1.

Aspect	Value
Pattern	BFS
Recognise it by	Multi-source BFS spreading in waves.
Time complexity	`O(mn)`
Space complexity	`O(mn)`
Difficulty	Medium

Who asks it

Companies known to ask this problem, from public LeetCode company-tag aggregations. A signal of where to expect it, not a guarantee.

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