The X-Wing technique is one of the most powerful advanced Sudoku solving methods. It's a fish pattern that can eliminate candidates and unlock progress in difficult puzzles. Understanding this technique will significantly improve your ability to solve challenging Sudoku puzzles.
What Is the X-Wing Pattern?
An X-Wing occurs when a specific number appears as a candidate in exactly two cells in two different rows (or columns), and these cells are also in exactly two different columns (or rows). This creates a rectangular pattern that looks like an "X" when you connect the corners.
How to Identify an X-Wing
To find an X-Wing pattern:
- Look for a specific number that appears as a candidate in exactly two cells in two different rows
- Check if these cells are also in exactly two different columns
- If they form a rectangle, you've found an X-Wing
How X-Wing Eliminates Candidates
When you find an X-Wing, you can eliminate the target number as a candidate from all other cells in the two columns (or rows) that contain the X-Wing. This is because the number must appear in one of the four corner cells of the X-Wing, making it impossible for it to appear elsewhere in those columns.
Example of X-Wing in Action
Imagine the number 7 appears as a candidate in cells (1,3), (1,7), (5,3), and (5,7). This forms an X-Wing pattern. You can then eliminate 7 as a candidate from all other cells in columns 3 and 7.
When to Look for X-Wing
X-Wing patterns typically appear in medium to difficult puzzles. Look for them when:
- You've exhausted basic techniques
- A number appears frequently as a candidate
- You're stuck and need a breakthrough
Practice Tips
To master the X-Wing technique:
- Practice on puzzles rated "Hard" or above
- Look for numbers that appear in exactly two cells per row/column
- Use pencil marks to track candidates
- Don't give up - X-Wing patterns can be subtle