Recognize this as a shortest path problem on an unweighted grid, so BFS is the optimal algorithm. Start BFS from the top-left cell, exploring all 4 directions level by level, and return the distance when reaching the bottom-right. Handle edge cases like blocked start/end or no path by returning -1.
Pro tip: Mention that BFS guarantees the shortest path in unweighted graphs, and proactively discuss space/time complexity (O(m*n)) and potential optimizations like bidirectional BFS or A* if the grid is huge.
Confirm grid dimensions, movement rules, and edge cases (e.g., start or end blocked, empty grid). Check if the start or end is 0 and immediately return -1.
Use a queue for BFS, starting with the top-left cell (0,0) and distance 0. Mark visited cells to avoid cycles, either by modifying the grid or using a separate visited set.
For each cell, check its 4-directional neighbors. If a neighbor is within bounds, walkable (1), and unvisited, add it to the queue with distance+1 and mark visited.
If the bottom-right cell is reached, return its distance. If the queue empties without reaching it, return -1.
State time and space complexity O(m*n). Optionally discuss bidirectional BFS or A* for large grids, and note that DFS would not guarantee shortest path.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.