aloalgoSudoku Solver
Fill a 9×9 grid so each row, column, and 3×3 box contains digits 1-9 exactly once.The Approach
- Find an empty cell
- Try digits 1-9
- Check if digit is valid (not in same row, column, or box)
- If valid, place it and recurse; if stuck, backtrack
Implementation
Optimized with Sets
Pre-compute empty cells and use sets for O(1) validity checks.Box Index Explained
The 9 boxes are numbered 0-8. For a cell at (row, col), the box index is calculated as:Complexity
- Time: O(9^empty_cells) in the worst case, but pruning makes it much faster in practice
- Space: O(1) for the basic version (modifying board in place), O(81) for the optimized version with sets
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