Classic backtracking problem and I'd seen it before, but I still fumbled the visited-cell tracking on my first pass.
Clarify the problem constraints (e.g., dictionary size, grid dimensions, movement rules) and then propose a backtracking DFS from each cell, using a trie to prune invalid prefixes. Optimize by marking visited cells and discussing trade-offs between trie and hash set approaches.
Pro tip: Mention that you would use a trie to avoid redundant searches and handle large dictionaries efficiently, and discuss how to handle duplicate words by using a set or marking trie nodes as visited.
Ask about grid size, dictionary size, allowed moves (8-directional?), and whether words can be reused. Confirm output format (list of words, order?).
Decide between a trie (for prefix pruning) or a hash set (for O(1) lookups). Explain why a trie is often better for large dictionaries.
Describe DFS backtracking from each cell, exploring neighbors, building strings, and checking against the dictionary/trie. Include visited marking to avoid cycles.
State time complexity: O(N * M * 4^L) worst-case without trie, but with trie it's O(N * M * 3^L) where L is max word length. Space: O(L) for recursion and O(total characters) for trie.
Discuss pruning (stop if prefix not in trie), deduplication (use set), and edge cases (empty grid, no words, single cell).
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