Classic Sudoku Puzzle

Classic Sudoku Puzzle turns number placement into a sequence of small deductions. Select an empty square and choose a digit, making sure the entry fits its row, column and three-by-three box. In the standard grid, each of those groups needs the digits one through nine without repetition. The useful question is not which digit looks plausible, but which digit survives all three restrictions.

Use temporary notes when several digits remain

The game's Mark function keeps candidate digits separate from confirmed answers. Use it to record the options that remain after checking a square's neighbors. When a final entry changes the row, column or box, review the notes in those groups. Outdated candidates can conceal a simple placement even when your earlier reasoning was sound.

Begin with a nearly complete group

Find a row or box with only a few missing digits, then compare its empty positions with their crossing groups. If only one candidate remains in a square, you have a reason to enter it. You can also search for a missing digit that has only one legal location within a group. Both methods make progress without guessing.

For worked examples, use the Sudoku deduction guide. The Sudoku collection provides related number challenges when you want another puzzle. Check each version's instructions before assuming it uses exactly the same grid or input method.