PIENSALIA / SUDOKU EDUCATION

Hidden Singles in Sudoku

A Hidden Single is a value with only one possible position in a row, column, or box.

Level: Learn how to find Hidden Singles by scanning rows, columns, and boxes for values with only one legal position.

Prerequisites

Know the three Sudoku rules and keep candidates consistent across each row, column, and 3 × 3 box.

How to apply it

1. Scan the relevant units and write only legal candidates.
2. Compare the positions or candidates described by the technique.
3. Make one justified placement or elimination.
4. Update related notes and rescan for new singles.

Worked example

A box can have four empty cells while the value 7 appears as a candidate in only one of them. That cell is the Hidden Single for 7.

Common mistakes

• Guessing before checking every related unit.
• Leaving stale candidates after a placement.
• Applying a pattern without verifying all of its positions.

When to use it

Use this scan when cells have several candidates but a unit still restricts one value to one position.