grid

A grid-traversal classic that tests BFS/DFS flood fill and the visited-marking discipline. The signal is treating the grid as a graph and counting connected components. Here is the answer.

The canonical grid DP where each cell depends on three neighbors at once. The signal interviewers want is the min-of-three recurrence, and the reason it has to be min. Here is the answer.

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