Enter your Sudoku puzzle into the grid below and click Solve to get the complete solution instantly. This solver uses a backtracking algorithm that can handle any valid 9x9 Sudoku puzzle, from easy to expert difficulty.
This solver uses a technique called backtracking, one of the most reliable algorithms for solving constraint-satisfaction problems like Sudoku. Here is how it works:
1. Find an empty cell. The algorithm scans the grid from left to right, top to bottom, looking for the first cell that has not been filled in.
2. Try each number. For that empty cell, it tries placing the numbers 1 through 9, one at a time.
3. Check validity. After placing a number, the algorithm checks whether it violates any Sudoku rules: no duplicate in the same row, column, or 3x3 box.
4. Recurse or backtrack. If the number is valid, the algorithm moves to the next empty cell and repeats. If no number from 1 to 9 works in a cell, the algorithm backtracks to the previous cell and tries the next candidate.
This process continues until every cell is filled (puzzle solved) or all possibilities are exhausted (no valid solution exists). While brute-force in nature, backtracking is extremely efficient for Sudoku because the constraints prune the search space dramatically.
Verify your solution. Finished a tough puzzle but not sure if it is correct? Enter it here to double-check.
Get unstuck. If you have been staring at a puzzle for too long, the solver can show you the answer so you can study the logic and learn from it.
Check puzzle validity. Not every arrangement of given numbers leads to a valid puzzle. Use the solver to confirm that a puzzle has a solution before sharing it.
Learn solving patterns. Compare the solved grid with the givens to understand which numbers depend on which constraints.