Sudoku Solver
Type the puzzle with the keyboard or paste it as 81 digits, using 0 or a dot for empty cells. The solver checks the puzzle, solves it and tells you how hard it is.
How to use it
- Type the digits into the grid or paste the whole puzzle.
- Press Solve.
- Read the solution, in blue, and the difficulty.
Frequently asked questions
How does the solver work?
It tries digits in the cell with the fewest candidates first and backtracks on contradictions, which solves even the hardest known puzzles in a few milliseconds. It keeps looking after the first solution to tell you if there is a second one.
Why must a Sudoku have a single solution?
A proper Sudoku has exactly one, so it can be solved by logic alone. It was proven in 2012 that at least 17 clues are needed for a unique solution.
How is difficulty rated?
The puzzle is solved again with human techniques only: single candidates, hidden singles, pairs and box-line eliminations. The last technique needed sets the level; if they are not enough, it is expert.