Classic backtracking problem and I knew it, but I still fumbled the visited-cell tracking for a second.
Use DFS with backtracking to explore all possible paths from each cell that matches the first character of the word. Mark cells as visited during the search and unmark them when backtracking to allow reuse in other paths. Return true if any path matches the entire word.
Pro tip: Before coding, discuss edge cases like empty board or word, and consider optimizations such as early termination if the word length exceeds the number of cells or if character frequencies don't match. This shows thoroughness and can impress the interviewer.
Ask clarifying questions about input constraints, character set, and expected output. Check edge cases like empty board or word, and validate if the word can possibly exist based on character counts.
Decide on DFS with backtracking as the primary approach. Explain why BFS is less suitable due to the need to track visited cells per path.
Write a recursive function that takes current position and index in word. Check boundaries, visited status, and character match. Mark cell as visited, recurse in four directions, then unmark.
Discuss time complexity O(N * 3^L) where N is number of cells and L is word length, and space complexity O(L) for recursion stack. Mention potential optimizations like early pruning.
Walk through a small example to verify correctness. Summarize the approach and mention any trade-offs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.