Classic BFS and I knew it immediately, which was both good and bad.
Clarify the problem constraints (e.g., grid size, whether diagonal moves are allowed) and edge cases (start or end blocked). Then explain that BFS is optimal for unweighted shortest path, and outline the algorithm with a queue and visited set, analyzing time and space complexity.
Pro tip: Mention that BFS guarantees the shortest path in an unweighted grid, and proactively discuss how you'd handle large grids (e.g., using a 2D array for visited instead of a set for efficiency).
Ask about grid size limits, whether start/end can be walls, and if moves are only 4-directional. Confirm return value for no path.
Explain that BFS explores level by level, so the first time you reach the target, it's the shortest path. Mention that DFS would not guarantee shortest path.
Use a queue initialized with start cell and distance 0. For each cell, check neighbors; if valid, unvisited, and open, enqueue with distance+1. Stop when target is reached.
Time and space are O(m*n) since each cell is visited at most once. Suggest using a 2D boolean array for visited and early exit when target is found.
Walk through a small grid (e.g., 3x3 with a wall) to demonstrate correctness, including a case with no path returning -1.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.