Determine whether a word can be formed by adjacent horizontal or vertical cells without reusing a cell.
A good solution should
- State the invariant or decision rule that makes the approach correct.
- Explain the time and space complexity in terms of the input sizes and required output.
- Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.
Reasoning prompt
Mark a cell as used during the current path and restore it during backtracking. Prune from letter counts or endpoint choice when useful.
Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.