Technique 01
Naked single
In row 1, the only digit missing is 4. After checking the column and box, cell r1c3 has just one legal candidate: 4.
How to play
Two singles worth learning well.
Classic Sudoku asks you to place digits 1–9 exactly once in every row, column, and 3 × 3 box. Printed givens stay fixed; every move below comes from those rules.
Technique 02
Hidden single
In row 2, digit 6 can go in only one cell: r2c1. That cell could hold other candidates, so the single is hidden in the row rather than exposed in the cell.
These worked states are the reviewed teaching fixtures used by the book layout specification. They are instructional examples, not sale claims.
Practice Help
The five-step checklist
- Scan: look for digits missing from a row, column, and box.
- List: choose an empty cell and write candidates that do not conflict with all three units.
- Single cell: if that cell has one candidate left, place it as a naked single.
- Single place: if a digit has only one legal place in a row, column, or box, place it as a hidden single.
- Update and repeat: check what changed, update candidates, and scan again; if stuck, revisit the examples and check for an incorrect note.
Use the controls without losing your place
The Easy samples include Notes, Erase, Undo, Redo, Check, Reveal solution, and Restart. Check marks incorrect entries without changing them. Reveal asks for confirmation and ends that attempt; Restart begins again from the printed givens.
Return to Easy practice