The diagonal part tripped me up at first because I had the standard 4-direction version basically memorized.
Use DFS/backtracking from each cell that matches the first character, exploring all 8 directions. Since cells can be reused, no visited set is needed, but be mindful of infinite loops if the word has repeated characters and the grid allows cycles. Optimize by pruning branches early and considering BFS if the word is long.
Pro tip: Clarify with the interviewer whether diagonal adjacency is truly allowed and whether cell reuse means unlimited reuse or just within a single path. This shows attention to detail and avoids incorrect assumptions.
Confirm adjacency definition (8-directional), cell reuse rules, and constraints (grid size, word length). Discuss edge cases like empty grid, empty word, or word longer than total cells.
Decide between DFS/backtracking and BFS. Since reuse is allowed, DFS with recursion is natural, but watch for cycles. Use a direction array for the 8 neighbors.
Iterate over each cell; if it matches word[0], start DFS. At each step, check bounds, character match, and recurse for the next character. Prune if index reaches word length (success).
Time complexity: O(N * M * 8^L) worst-case, where L is word length. Discuss potential optimizations like early termination, memoization (if reuse not allowed), or bidirectional search.
Walk through examples, including cases with reuse and diagonal moves. Test edge cases like single-character word, no match, and large grids.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.