Check whether the filled cells violate any row, column, or 3-by-3 box uniqueness rule; empty cells are ignored.
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
Validate each constraint independently and avoid treating the puzzle’s eventual solvability as part of this check.
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.