How does the solver work?

The solver uses a backtracking algorithm: it tries placing digits 1–9 in each empty cell, checks whether the placement is valid (no duplicate in row, column, or 3×3 box), and recursively continues. If it reaches a dead end it backtracks and tries the next digit.

Can the solver handle any Sudoku puzzle?

Yes, as long as the puzzle is valid — meaning it has at most one solution. If a puzzle has multiple solutions, the solver returns the first one it finds. Invalid puzzles (contradictory clues) are flagged with no solution.

What if the solver says 'No solution'?

This means the clues you entered contain a contradiction — for example, two identical digits in the same row, column, or box. Check your input carefully, or press Clear and start again.

Are the random puzzles unique?

Random puzzles are generated with a unique solution. The generator fills a solved grid randomly and then removes cells while ensuring the puzzle remains solvable with exactly one solution.

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Sudoku Solver

Solve any Sudoku puzzle instantly or generate a new one to practice.

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Sobre esta ferramenta

An interactive Sudoku solver that uses a backtracking algorithm to find the solution to any valid 9×9 Sudoku puzzle. Enter your puzzle by clicking cells and typing numbers, then press Solve to fill in the answer. Original numbers are shown in black, solver-filled numbers in blue, and invalid entries in red. Use the Random Puzzle button to generate a new solvable puzzle with pre-filled clue cells. Check validates your current progress without revealing the full solution. All logic runs entirely in your browser — no data is sent to any server.

Como usar

1 Click a cell in the grid and type a number from 1 to 9.
2 Fill in the clues you know from your puzzle.
3 Press Check to highlight any conflicts in red.
4 Press Solve to automatically fill in the complete solution.
5 Press Random Puzzle to load a new practice puzzle.
6 Press Clear to reset the entire board.

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