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This one took me a minute to even figure out where to start.
Use a Trie to store the dictionary for efficient prefix lookups, then perform DFS from each cell on the board, exploring all 8 directions while marking visited cells. As you traverse, check if the current prefix exists in the Trie; if it's a complete word, add it to the result set. This prunes branches early and avoids redundant searches.
Pro tip: Mention that you can optimize by removing words from the Trie once found to avoid duplicates, and discuss trade-offs between using a Trie vs. a HashSet with prefix checking. Also, clarify assumptions about board size, dictionary size, and whether words can be reused (typically not).
Ask about board dimensions, dictionary size, whether words can be formed using the same cell multiple times (usually no), and if the output should be sorted or unique. This shows attention to detail.
Decide to use a Trie for the dictionary to enable O(1) prefix checks, and a 2D boolean array to track visited cells during DFS. Alternatively, a HashSet with prefix checking can work but is less efficient.
For each cell, start a DFS that explores all 8 neighboring cells, building the current string. At each step, check if the current prefix exists in the Trie; if not, backtrack. If it's a complete word, add to results.
Use a set to store found words to avoid duplicates. Optionally, remove words from the Trie once found to prune further searches. Discuss time complexity: O(N*M*8^L) worst-case, but Trie pruning reduces it.
Walk through a small board and dictionary, including cases with no words, single-letter words, and words that require revisiting cells (which should be disallowed).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.