OneTaskBy Tim King · Updated
Sudoku Solver
Paste a Puzzle and Spot Clashing Digits, No-Solution and Multiple-Answer Grids
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How the Sudoku Solver works
This sudoku solver fills in any standard 9×9 puzzle. Type the givens straight into the grid, or paste the puzzle as 81 characters, and the answer appears in orange in every empty square. Untick "Show solution" to hide it again and use the grid to check your own progress.
How to enter a puzzle in the sudoku solver
Click a square and type its digit. The arrow keys move around the grid, and Backspace clears a square. To paste a puzzle instead, put it in the text box as nine rows of nine, using a digit for each given and a dot or zero for each blank. Spaces, line breaks and other separators are ignored, so most puzzles copied from a website or an app paste in cleanly.
What the checks mean
Two copies of a digit in the same row, column or box are marked in red, because no solution can exist until one of them is fixed. If the clues are legal but still lead nowhere, the solver says the puzzle has no solution. If it finds two different solutions, it tells you the puzzle is not a proper sudoku, which usually means a clue was missed when copying.
Singles and search
The stats show whether the puzzle falls to singles alone, meaning every square can be filled by spotting the only place a digit fits. Puzzles that need more than that are harder by hand. The search step count shows how much trial and error the computer needed.
FAQ
Can it solve the hardest sudoku puzzles?
Yes. It combines constraint checking with a full search, so even puzzles built to defeat human solvers finish in a fraction of a second. Puzzles with very few clues may have several solutions, and the solver tells you when that happens.
Does it show the steps?
It shows the finished grid rather than a step-by-step path. The stats say whether simple singles are enough to solve it, which is a good guide to whether a stuck puzzle needs a more advanced technique such as pairs or X-wings.
Can I use it to check my answers without spoiling the puzzle?
Yes. Untick "Show solution" and type your digits into the grid. Any digit that clashes with another in its row, column or box turns red, and the note at the top says when every square is filled correctly.
See also: all Puzzle Solvers tools, Scrabble & Board Games, Anagrams & Rhymes, Puzzle Makers.
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