My first instinct was to just count edges per cell and sum them up, which is the right direction, but I kept second-guessing myself on whether to use BFS or DFS to group cells per island.
Use DFS or BFS to traverse each island, computing its perimeter by counting the four edges of each land cell that are either out of bounds or adjacent to water. Track the maximum perimeter across all islands and return 0 if no land is found.
Pro tip: Clarify edge cases upfront (e.g., empty grid, all water, single cell) and mention that you can compute perimeter during traversal without extra space, showing attention to efficiency.
Confirm that islands are connected horizontally/vertically, and that perimeter is the total number of exposed edges. Discuss edge cases like empty grid, no land, and single cell.
Decide between DFS (recursive or iterative) and BFS. Mention that DFS is often simpler for grid traversal, but be prepared to discuss trade-offs like recursion depth.
For each land cell, check its four neighbors. If a neighbor is out of bounds or water, increment the perimeter by 1. Avoid double-counting by marking visited cells.
Maintain a global variable for the maximum perimeter found so far. After traversing each island, update the maximum if the current island's perimeter is larger.
State that time complexity is O(m*n) since each cell is visited once, and space complexity is O(m*n) in the worst case for the visited set or recursion stack. Mention potential optimizations like modifying the grid in-place to avoid extra space.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.