I jumped to DFS pretty fast which was the right call, but I fumbled the visited-cell logic at first.
Use depth-first search (DFS) with backtracking to explore all possible paths from each cell that matches the first character of the word. At each step, mark the current cell as visited, recursively search its four neighbors for the next character, then unmark it to allow other paths. Return true if any path matches the entire word.
Pro tip: Clearly explain how you avoid revisiting cells (e.g., by temporarily modifying the grid or using a visited set) and discuss the time complexity (O(N * 3^L) where N is the number of cells and L is the word length). Mentioning pruning techniques like checking character frequency upfront can show deeper optimization thinking.
Confirm the problem constraints: grid dimensions, character set, word length, and whether diagonal moves are allowed. Ask if the grid can be modified in-place.
Select DFS with backtracking as the primary approach. Explain why BFS is less suitable due to the need to track visited cells per path.
Iterate over each cell; if it matches the first character, start DFS. In DFS, check if the current index equals word length (success). Mark cell visited, explore four directions recursively, then unmark.
Discuss pruning: pre-check if the word's character counts exceed the grid's. Analyze time and space complexity, and mention iterative deepening if relevant.
Walk through examples, including empty word, single-cell grid, and cases where the word is longer than the number of cells. Verify backtracking correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.