Advanced Sudoku Techniques: How to Spot and Use the X-Wing
Quick answer: The X-Wing is an advanced elimination technique. When one candidate number appears exactly twice in two rows and those cells share the same two columns, they form a rectangle — and you can remove that candidate from everywhere else in those two columns (or rows).
You’ve filled out your pencil marks, cleared the naked pairs, and yet the grid remains completely locked. Welcome to advanced Sudoku. To solve expert-level puzzles, you have to look for interconnected logic across the entire board.
The most famous—and satisfying—advanced technique is the X-Wing. Here is how to spot it and use it to break open tough grids.
What is an X-Wing?
The X-Wing is an elimination strategy based on a single number across four cells that form the corners of a rectangle.
It occurs when a specific candidate number appears exactly twice in two different rows (or columns), and those candidates align perfectly in the same columns (or rows).
How to Find an X-Wing Step-by-Step
Let’s say we are looking for the number 4:
- Find Row A: You notice that the number
4can only fit into two cells in Row 2: Column 3 and Column 8. - Find Row B: You scan down and notice that in Row 7, the number
4also fits only in Column 3 and Column 8. - Visualize the Rectangle: Connect these four cells in your mind. They form a perfect rectangle.
Because of how Sudoku works, if the 4 in Row 2 goes into Column 3, then the 4 in Row 7 must go into Column 8 (and
vice versa). They form a diagonal cross—hence the name “X-Wing.”
The Payoff: Making the Elimination
Because the number 4 is guaranteed to be in either the left or right corners of this rectangle, no other cell in
Column 3 or Column 8 can contain a 4.
The Golden Rule: If you found the X-Wing using rows, you eliminate candidates from the intersecting columns.
By clearing out those extra candidates, you will instantly create “naked singles” or clear paths to solve the surrounding blocks.
Ready for Evil Mode?
Once you master the X-Wing, look up the Swordfish—it operates on the exact same logic, but uses a 3x3 grid of intersecting rows and columns instead of 2x2!