Naked Single Technique: The Most Direct Sudoku Solving Method
Naked Single, also known as "Sole Candidate", is the most basic and direct Sudoku solving technique. The core idea is simple: when a cell has only one candidate number remaining, that number is the answer.
Sudoku rules require each cell to contain a number from 1-9, with no duplicates in the same row, column, or box. When we discover through elimination that a cell can only contain one number, that number is the definite answer.
Before reading this article, we recommend understanding Sudoku naming conventions.
Naked Single Example
In the image above, cell D8 has only one remaining candidate: 1. This means:
- Numbers 2-9 have been eliminated due to existing numbers in the same row, column, or box
- Only number 1 can be placed in this cell
- Therefore, D8 = 1
Because the single candidate is "naked" or exposed - you can directly see that only one number remains in the cell without analyzing the entire row, column, or box. The answer is right there in plain sight!
Naked Single vs Hidden Single
Naked Single and Hidden Single are the two most fundamental Sudoku techniques. Let's compare them:
In the image above, cell E7 has candidates 1, 2, 3, 4, 7. However, looking at Box 8, only E7 contains candidate 4. Therefore, E7 = 4.
| Comparison | Naked Single | Hidden Single |
|---|---|---|
| Focus | Single cell | Entire row/column/box |
| Criteria | Cell has only 1 candidate | Number has only 1 position in unit |
| Candidates | Cell shows only 1 number | Cell may show multiple numbers |
| Difficulty | Easier to spot (look at cell) | Requires scanning entire unit |
- Naked Single: Look at the cell → What can this cell be?
- Hidden Single: Look at the number → Where can this number go?
Practical Tips
1. Use Candidate Notation
To effectively use Naked Single, properly mark candidates. When you note all possible numbers for each empty cell, Naked Singles will automatically appear - cells with only one candidate are your answers.
2. Update Candidates Promptly
After filling in a number, remember to update related cells' candidates. This may create new Naked Singles.
3. Combine Both Techniques
In practice, Naked Single and Hidden Single are often used alternately. Filling in one number may create both situations.
Start a Sudoku game and try the Naked Single technique!