1582 articles
Solve LeetCode 733 Flood Fill with simple DFS in O(m*n) time. The paint bucket tool from MS Paint reduced to a five-line recursion — the cleanest introduction to grid traversal you can give an interviewer.
Solve LeetCode 463 Island Perimeter in O(m*n) without DFS or BFS. The trick: every land cell contributes 4 edges, minus 2 for each shared edge with another land cell. Pure counting beats traversal.
Find the maximum area of any island in a binary grid using DFS that returns the size of each connected component. The canonical "DFS with return value" pattern asked at Google, Meta, and Amazon.
Capture every region of Os surrounded by Xs by inverting the problem — flood from the boundary instead of the interior. The classic boundary-DFS pattern interviewers love.
Compute the minimum minutes for rot to spread across a grid using multi-source BFS. The canonical "all sources start at the same time" pattern that solves dozens of grid-spreading problems.