Beginner Lesson 2 of 4

Basic Singles

The foundation of all Sudoku solving. Master these two essential techniques and you'll be able to solve many easy and medium puzzles.

01Naked Singles 02Hidden Singles Key Differences
1

Naked Singles

A naked single occurs when a cell has only one possible candidate remaining. This is the most basic and important solving technique.

Worked example

Naked Single in Action

1

Cell Identification

"This cell only has one candidate"

Magic Sudoku highlights the cell that can only contain one number based on the current pencil marks.

2

Constraint Analysis

"We can rule out every other number by looking at the row, column, or box"

Shows you exactly which placed numbers eliminate the other possibilities, leaving only one valid option.

3

Solution

"Therefore, this cell must be [number]"

Places the number and automatically updates pencil marks throughout the grid.

When to use

  • Look for cells with only one candidate remaining
  • Check cells whose row, column, and box together already contain 8 different numbers
  • Always start with this technique—it's the most straightforward

Vocabulary tip

Notice how we use candidates and houses? These key terms from our glossary help describe exactly what's happening in each technique. Familiarizing yourself with these terms makes learning advanced strategies much easier!

2

Hidden Singles

A hidden single occurs when a number can only go in one place within a row, column, or box, even if that cell has multiple candidates.

Worked example

Hidden Single in Action

1

Missing Number

"We are missing a 9 in this row"

Magic Sudoku highlights the entire unit that needs the missing number.

2

Restriction Analysis

"These 9's affect this row"

Shows which placed numbers restrict where the missing number can go.

3

Elimination

"So, these cells cannot be 9"

Eliminates the impossible locations, leaving only one option.

4

Solution

"Therefore, this cell must be 9"

Places the number in the only remaining valid position.

When to use

  • Scan each row, column, and box for missing numbers
  • Check if a missing number can only fit in one cell of that unit
  • Often more powerful than naked singles in advanced puzzles

Side by side

Key Differences

Naked Singles

Focus
Individual cells
Look for
Cells with one candidate
Spotting
Usually easier
Approach
Bottom-up

Hidden Singles

Focus
Missing numbers
Look for
Numbers with one location
Spotting
Requires systematic scanning
Approach
Top-down

Ready to Practice?

These two techniques form the foundation of all Sudoku solving. Master them, and you'll be ready to tackle more advanced strategies.

Practice with Magic Sudoku