1582 articles
Find every cell from which water can flow to both oceans by reversing the flow and running DFS inward from each ocean. The reverse-flow trick that turns an O(N^4) brute force into O(N^2).
Find the shortest clear path from top-left to bottom-right in a binary grid with 8-directional movement. Pure BFS on an unweighted graph — the classic shortest-path-in-a-grid interview problem.
Find the water cell whose distance to the nearest land is maximized. Multi-source BFS from all land cells gives the answer in linear time — a top FAANG distance-spread problem.
Determine whether a word can be spelled by traversing adjacent cells without reusing any cell. The canonical DFS-with-backtracking template every grid-search interview problem builds on.
Count islands with unique shapes by encoding each DFS traversal path as a string and storing shapes in a set. A classic interview problem testing DFS + hashing.