Naked Single in Sudoku
A naked single is the simplest fully determined move in Sudoku. Once every conflicting digit has been ruled out and only one candidate remains in a cell, that value must be placed with no guesswork.
Summary
Find cells with one remaining candidate and place them with confidence.
Table of Contents
What this technique is
A naked single is a cell with exactly one candidate left after row, column, and box eliminations are applied.
When to use it
Use constantly while scanning. It is common in easy and medium boards and appears in harder puzzles after candidate cleanup.
How it works
For one cell, eliminate values present in its row, column, and box. Place the remaining value when only one candidate is left.
Step-by-step
- Select an empty cell.
- Remove row, column, and box conflicts.
- Place the only remaining candidate.
Example
If a cell cannot be 1-7 or 9 due to row/column/box conflicts, then 8 is forced as a naked single.
Naked Single vs Hidden Single
Naked single means one cell has one value left. Hidden single means one digit has one legal location in a row, column, or box.
Example
If row and column constraints remove every option except 8 from one cell, that cell is a naked single and must be 8.
Common Mistakes
- Not checking all three constraints before placing.
- Placing a value before validating row, column, and box together.
- Ignoring updates in nearby cells after placement.
- Missing singles because notes are outdated.
- Forgetting to remove stale candidates after each confirmed placement.
FAQ
What is a naked single?
A naked single is a cell where exactly one candidate remains.
Is a naked single easier than a hidden single?
Usually yes, because it can be determined from one cell.
Do naked singles appear in expert puzzles?
Yes. They often appear after advanced eliminations open up the grid.