Naked Single Sudoku Strategy
Naked singles are the most basic and essential Sudoku solving technique. This strategy is often the first step in solving any puzzle and forms the foundation for more advanced methods.
A naked single occurs when a cell in the Sudoku grid has only one possible candidate left after considering the numbers already present in its row, column, and 3x3 box. When this happens, you can confidently fill in that cell with the remaining number.
What is a Naked Single?
A naked single is present when, after eliminating all numbers already used in the same row, column, and box, only one candidate remains for a cell. This means that the value of the cell is determined by the process of elimination.
How to Spot a Naked Single
To find a naked single, scan the grid for cells that have only one possible candidate. This can be done by:
- Looking at each empty cell and listing all possible numbers that could go there.
- Eliminating candidates that already appear in the same row, column, or box.
- If only one candidate remains, that cell is a naked single and can be filled in immediately.
Example:
If a cell in row 4, column 7 can only be a 5 (because 1-4, 6-9 are already present in its row, column, or box), then 5 is a naked single for that cell.
Why Use the Naked Single Technique?
The naked single technique is crucial for making progress in any Sudoku puzzle, especially at the beginning. It helps you fill in certain values with complete confidence and often leads to a cascade of further naked singles as the puzzle unfolds.
Naked Single Example
Let’s walk through an example of how to identify and fill in a naked single.
Suppose you are solving a puzzle and notice that in a particular cell, after checking its row, column, and box, only the number 7 is missing. Since no other candidates are possible, you can immediately place 7 in that cell.
After filling in the naked single, check the surrounding cells again—often, solving one naked single will reveal others nearby.
Tips for Using Naked Singles
- Regularly scan the grid for cells with only one candidate.
- Each time you fill in a naked single, update the candidates for all affected cells.
- Naked singles can appear at any stage of the puzzle, so keep looking for them as you progress.
You’ve now learned how to spot and use the naked single technique. Try it out in your next Sudoku game and see how quickly you can make progress!