Sudoku has just three simple rules, but they create endless logical challenges.
Understanding the Concept
Rule 1: Each row must contain the digits 1-9 with no repetition.
Rule 2: Each column must contain the digits 1-9 with no repetition.
Rule 3: Each 3×3 box must contain the digits 1-9 with no repetition.
That's it! These three rules are all you need to know to solve any Sudoku puzzle.
Every valid Sudoku puzzle has exactly one solution that can be reached through logical deduction.
Examples
Valid Placement
The 6 at R0C2 (green) is valid: 6 doesn't appear anywhere else in row 0, column 2, or the top-left box.
5
3
6
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
Solution
Invalid Placement
Placing a 5 at R0C2 would be wrong (red) because 5 already exists at R0C0. Two 5s in the same row violates Rule 1.
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
Eliminated
Pro Tips
- •If a number appears in a row, it cannot appear again in that same row
- •If a number appears in a column, it cannot appear again in that same column
- •If a number appears in a box, it cannot appear again in that same box
- •Use these constraints to eliminate possibilities and find the right numbers
