Sudoku Solving Techniques

Technique guides

Each guide includes an interactive, step-through example board.

Beginner techniques

Scanning and cross-hatching

Choose one digit and inspect a 3×3 box. Existing copies of that digit in crossing rows and columns eliminate cells until its position becomes clear. Practise this on an Easy Sudoku.

Naked singles

When every candidate except one has been eliminated from a cell, the remaining digit is certain. Keeping complete notes makes naked singles visible.

Hidden singles

A digit may have only one legal location in a row, column or box even when that cell has other candidates. Scan one unit and one digit at a time.

Try it: find the hidden single

Intermediate techniques

Naked pairs

If two cells in one unit contain the same two candidates, those digits must occupy those cells. Remove both candidates from every other cell in that unit.

Pointing pairs and triples

If all candidates for a digit inside a box lie on one row or column, that digit cannot appear elsewhere on the same row or column outside the box.

Box-line reduction

If every candidate for a digit in a row or column lies inside one box, eliminate that digit from the other cells in the box.

Advanced patterns

Patterns such as X-Wing, Swordfish and XY-Wing use candidate relationships across several units. Start with accurate notes and master pairs and box-line interactions before relying on these patterns. Practise on Hard or Expert Sudoku.

Keep learning through play

The best technique is the simplest one that proves the next placement. Start with scanning, update notes after every digit and escalate only when basic deductions stop producing progress.