1. What Exactly is an X-Wing?
An X-Wing pattern occurs when a candidate number (for example, the digit 7) appears in strictly two cells in each of two different rows, and those four cells share the exact same two columns.
Geometric X-Wing Pattern for Digit 7:
Col 2 Col 8
Row 2: [ 7 ] ------------ [ 7 ] (Row 2 has 7 only here)
| \ / |
| \ / |
| X |
| / \ |
| / \ |
Row 7: [ 7 ] ------------ [ 7 ] (Row 7 has 7 only here)
Row 2: [ 7 ] ------------ [ 7 ] (Row 2 has 7 only here)
| \ / |
| \ / |
| X |
| / \ |
| / \ |
Row 7: [ 7 ] ------------ [ 7 ] (Row 7 has 7 only here)
Because each row must contain a 7, the digit 7 must occupy either (Top-Left + Bottom-Right) OR (Top-Right + Bottom-Left). Either way, columns 2 and 8 are guaranteed to have their 7s in one of these four corner cells!
2. The Elimination Action (The Payoff)
Since the digit 7 is permanently claimed by the four corner squares in Columns 2 and 8:
Golden Rule of X-Wing:
You can eliminate candidate 7 from ALL OTHER cells in Column 2 and Column 8 across the entire rest of the board!
3. How to Find an X-Wing (3-Step Checklist)
- Filter single numbers: Tap a number (e.g. 7) to highlight all cells containing candidate notes for that number.
- Scan for 2-candidate lines: Find two rows that each hold only two instances of that candidate.
- Verify parallel columns: Check if the column coordinates align into a rectangle. If they do, strike out all other candidates in those two columns!
Ready to Practice X-Wings?
Play Hard or Expert Sudoku on iLoveSudoku with smart highlights that help you visualize candidate lines.