How to Play Sudoku
Sudoku is a logic-based number placement puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids contains all of the digits from 1 to 9.
- 1Each row must contain the numbers 1-9, without repetition
- 2Each column must contain the numbers 1-9, without repetition
- 3Each 3×3 box must contain the numbers 1-9, without repetition
- 4The puzzle setter provides a partially completed grid with a unique solution
- 5No guessing is required - every puzzle can be solved through logical deduction
Naked Singles
When a cell can only contain one possible number, that number must be placed there. This is the most basic technique and should always be checked first.
Hidden Singles
When a number can only go in one cell within a row, column, or box, even if that cell has other candidates, that number must be placed there.
Naked Pairs
When two cells in the same row, column, or box can only contain the same two numbers, those numbers can be eliminated from other cells in that unit.
Pointing Pairs
If a number in a box is restricted to one row or column, that number can be eliminated from the rest of that row or column outside the box.
Box/Line Reduction
If all occurrences of a number in a row or column are confined to one box, that number can be eliminated from other cells in that box.
X-Wing
An advanced technique where a number appears in only two positions in two different rows (or columns), forming a rectangle. This allows elimination of that number from other cells in those columns (or rows).
Swordfish
An extension of X-Wing using three rows and three columns. When a number is confined to three cells in each of three rows, aligned in three columns, it can be eliminated from other cells in those columns.
- •Start with easier puzzles and gradually increase difficulty
- •Scan for naked singles first - they are the quickest to spot
- •Focus on rows, columns, or boxes with the most filled cells
- •Use pencil marks (candidates) to track possible numbers in each cell
- •Look for numbers that appear frequently in the grid
- •Take breaks if you get stuck - fresh eyes often spot what you missed
- •Practice regularly to improve your pattern recognition
- •Don't guess - if you can't logically deduce a number, look for a different approach