grid

A staple grid-traversal problem probing BFS/DFS flood fill and disciplined visited-marking. What interviewers watch for: viewing the grid as a graph and tallying connected components. Here is the answer.

The textbook grid DP where each cell depends on three neighbors at once. What interviewers want is the min-of-three recurrence, plus the reason it has to be min. The answer follows.

The rotting-oranges family of build screens: a state expands outward one step per tick across a grid, with the spec adding rules each round. The signal is multi-source BFS processed by layers, not per-cell loops. Here is the design that absorbs each new test case.