📘 Sudoku Strategies

Sudoku is best solved with consistent logic. The strategies below are common techniques used to make progress without guessing, from basic singles to advanced pattern eliminations.

Beginner: Singles and Scanning

Start with the simplest moves. Many puzzles open up quickly once you identify forced placements.

Naked Single

A naked single is a cell with only one valid candidate after checking its row, column, and 3×3 box. When only one number is possible, you can place it immediately.

Hidden Single

A hidden single occurs when a specific number can only go in one cell within a row, column, or box—even if that cell currently has multiple candidates. Scanning one number at a time often reveals hidden singles.

Intermediate: Pairs and Locked Candidates

When singles run out, the next step is narrowing candidates using relationships between cells.

Naked Pairs (and Triples)

If two cells in the same row, column, or box contain the same two candidates, those candidates must occupy those two cells. You can remove those numbers from the candidate lists of all other cells in that unit.

Locked Candidates

If a candidate within a 3×3 box is restricted to a single row or column, it cannot appear elsewhere in that row or column outside the box. This technique often unlocks new singles.

Advanced: Pattern Techniques

Harder puzzles may require pattern-based eliminations. These techniques are not always necessary, but they can help you progress when simpler methods stall.

X-Wing

An X-Wing forms when a candidate appears in exactly two positions in two different rows (or columns), and those positions align in the same two columns (or rows). In that case, the candidate can be eliminated from other cells in the matching columns (or rows).

Swordfish

Swordfish extends the X-Wing concept across three rows and three columns. When a candidate is limited to the same three columns across three rows (or vice versa), you can eliminate it from other cells in those columns.

A consistent process

After every placement, rescan the affected row, column, and box. Sudoku solving is often a loop: eliminate candidates, place forced numbers, and repeat. With practice, these strategies become quick pattern recognition.