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Naked Singles Strategy

BeginnerFundamental Technique

What is a Naked Single?

A Naked Single is the most basic Sudoku solving technique. It occurs when a cell has only one possible value, based on the numbers already present in its row, column, and box.

This technique is called "naked" because the single candidate is directly visible without needing to consider other cells' candidates.

Naked Singles are often the first technique you'll use when solving a Sudoku puzzle, and they're essential for making progress in puzzles of any difficulty level.

How to Find Naked Singles

  1. 1. Select an empty cell

    Start by focusing on one empty cell in the puzzle that you want to solve.

  2. 2. Identify existing numbers

    Look at all the numbers that already appear in the same row, column, and 3×3 box as your selected cell.

  3. 3. Determine possible values

    List all the numbers from 1-9 that do NOT appear in the related row, column, and box. These are the possible values for your cell.

  4. 4. Check for a single possibility

    If there's only one number in your list of possible values, you've found a Naked Single! This number must go in that cell.

Example

Before

In this example, look at the highlighted cell in the middle box. Let's determine what number must go there.

5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9

Analysis

Let's check what numbers are already present in:

  • Row 5: 4, 8, 3, 1 are present
  • Column 5: 7, 9, 6, 2, 1, 8 are present
  • Box (middle): 8, 6, 3, 2 are present

Combining these constraints, the numbers 1, 2, 3, 4, 6, 7, 8, 9 are all eliminated as possibilities.

Therefore, 5 is the only possible value for this cell - a Naked Single!

When to Use This Technique

  • At the beginning of solving any Sudoku puzzle
  • After applying any other technique that eliminates candidates
  • When you're stuck and need to find the next move

Pro Tip: Always look for Naked Singles before applying more complex techniques. They are the easiest to spot and can often lead to a chain reaction of additional Naked Singles.

Practice This Technique

Try finding all the Naked Singles in this puzzle to improve your skills.

Related Strategies

Difficulty Level

BeginnerAdvanced

Naked Singles is a fundamental technique that's essential for solving puzzles of all difficulty levels. It's the first technique every Sudoku player should master.