Sudoku365
X-Wing Pattern Strategy
The X-Wing is one of the most powerful advanced Sudoku techniques. It's called "X-Wing" because the pattern forms an X shape on the grid. This technique is essential for solving expert-level puzzles.
What is an X-Wing?
An X-Wing occurs when a candidate number appears in exactly two cells in each of two rows (or two columns), and these cells are aligned to form a rectangle.
The X-Wing Pattern
Consider rows A and B, where the number 5 can only appear in columns 3 and 7:
- Row A: 5 can be in column 3 or column 7
- Row B: 5 can be in column 3 or column 7
This creates four cells forming a rectangle. The key insight: 5 must appear exactly once in column 3 and once in column 7.
The Elimination
Because we know 5 must occupy one cell in column 3 and one in column 7, we can eliminate 5 as a candidate from all other cells in those columns (except the four X-Wing cells).
How to Identify X-Wings
- Choose a candidate number (e.g., 5)
- Find two rows where that number appears in exactly two cells each
- Check if these cells align in the same columns (forming a rectangle)
- If yes, eliminate that number from all other cells in those two columns
Column-Based X-Wings
X-Wings can also work with columns:
- Find two columns where a number appears in exactly two cells each
- Check if these cells align in the same rows
- Eliminate that number from other cells in those rows
Common Mistakes
- More than two cells: X-Wing requires exactly two cells per row/column. If there are three, look for Swordfish instead
- Wrong elimination direction: Row-based X-Wings eliminate from columns; column-based X-Wings eliminate from rows
- Misaligned cells: The four cells must form a perfect rectangle
When X-Wings Appear
X-Wings typically appear in:
- Expert-level puzzles
- Difficult hard puzzles
- Puzzles that seem "stuck" after basic techniques
Related Techniques
Practice
- Expert puzzle - likely to require X-Wing
- Hard puzzle - may contain X-Wing opportunities