Sudoku is a logic-based number puzzle that follows specific rules to ensure a unique solution. Understanding these 12 fundamental rules is essential for both solving puzzles and creating valid Sudoku grids.
The 12 Core Rules of Sudoku
Basic Grid Rules (3 rules)
- Row Rule: Each row must contain all numbers 1-9 exactly once
- Column Rule: Each column must contain all numbers 1-9 exactly once
- Box Rule: Each 3x3 box must contain all numbers 1-9 exactly once
Solving Rules (3 rules)
- Single Candidate: If a cell has only one possible number, it must be that number
- Single Position: If a number can only go in one cell within a row, column, or box, place it there
- Elimination: Use the three basic rules to eliminate impossible candidates from cells
Advanced Solving Rules (3 rules)
- Pairs and Triples: When two or three cells contain the same candidates, eliminate those candidates from other cells in the same unit
- Hidden Singles: Look for numbers that can only appear in one cell within a row, column, or box
- Naked Singles: Fill cells that have only one remaining candidate
Pattern Recognition Rules (3 rules)
- X-Wing: When a digit appears in exactly two cells in two rows and those cells are in the same columns, eliminate that digit from other cells in those columns
- Swordfish: An extension of X-Wing involving three rows and three columns
- XY-Wing: A pattern where three cells form a chain that allows elimination of a candidate
Why These Rules Matter
These 12 rules form the complete foundation of Sudoku solving. The first three are the basic constraints that define what makes a valid Sudoku puzzle. Rules 4-6 are the fundamental solving techniques every player should master. Rules 7-9 introduce intermediate strategies, while rules 10-12 are advanced techniques for difficult puzzles.
Applying the Rules
Start with the basic rules (1-3) to understand the puzzle structure. Then apply solving rules (4-6) systematically. As puzzles become more challenging, incorporate advanced rules (7-9) and pattern recognition (10-12). Remember, the goal is to use these rules to eliminate possibilities until only one number remains for each cell.