My first instinct was BFS and I think that was right, but I fumbled the neighbor comparison for a bit.
Model the terrain as a graph where each cell is a node with directed edges to lower or equal-height neighbors, then perform a traversal (BFS/DFS) from the starting point to find all reachable cells. Clarify edge cases like equal heights, boundaries, and whether water can flow diagonally before coding.
Pro tip: Discuss both BFS and DFS, but recommend BFS for its iterative nature and ability to stop early if only a count is needed. Also, mention that if the start is a local minimum, only that cell gets wet, and confirm whether water can flow to equal-height neighbors.
Ask about grid size, height range, flow rules (diagonal? equal heights?), and whether the start cell is always wet. Confirm output format (list of cells or count).
Treat each cell as a node with edges to neighboring cells of lower or equal height. Use BFS or DFS from the start to find all reachable cells.
Select BFS for level-order exploration and easy cycle handling, or DFS for simplicity. Explain time and space complexity: O(R*C) time and space in the worst case.
Consider start at boundary, start as local minimum, equal-height plateaus, and disconnected regions. Ensure visited set prevents infinite loops.
Walk through a small example, then discuss potential optimizations like early termination if only count is needed, or using union-find for offline queries.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.