X-Wing
A digit restricted to exactly two cells in two different rows, forming a rectangle.
Also known as: 2-Fish, Fish Pattern, Conjugate Pair Rectangle
Quick Summary
An X-Wing occurs when a candidate digit appears exactly twice in two different rows, and those candidate cells align in the same two columns, allowing eliminations across both columns.
Understanding the X-Wing Technique
The X-Wing is the most famous advanced Sudoku technique and the foundation of all 'fish' patterns (2-fish). It bridges the gap between single-house logic and grid-wide geometric deductions. When a digit is forced into one of two positions in two parallel lines (e.g. rows), and those positions line up across the same perpendicular lines (columns), they form a rectangle with diagonal options. Whichever diagonal contains the true digit, each column receives exactly one occurrence, meaning that digit can be completely eliminated from all other cells in those columns.
Visual Examples
Green cells highlight the X-Wing pattern, amber cells denote where candidates are affected, and struck-through pencil marks show the eliminations. Use the buttons or arrow keys to browse examples.
How to Spot & Solve a X-Wing (Step-by-Step Guide)
The complete visual scanning and logical deduction process to execute this technique:
- 1Pick a candidate digit and find two different rows where that digit appears in exactly two cells.
- 2Check that the candidate cells in both rows line up in the exact same two columns, forming a rectangle.
- 3In the first row, the digit must go in either the left corner or the right corner.
- 4If it lands in the left corner of the first row, it is forced into the right corner of the second row (and vice versa).
- 5Either diagonal pair forces exactly one placement in each of the two columns.
- 6Safely erase that candidate from all other cells along both columns.
Common Traps & Mistakes to Avoid
- Allowing a third candidate in one of the base rows. The base rows MUST have exactly two candidate cells.
- Eliminating from the base rows instead of the crossing columns.
- Assuming the four cells must be in the same box. In fact, an X-Wing never sits in a single box (that would just be locked candidates).
Frequently Asked Questions
Can an X-Wing be column-based?
Yes! If two columns have the target candidate in exactly two rows, that candidate can be eliminated from all other cells in those two rows.
Does an X-Wing immediately place a number?
Usually not directly. It eliminates candidates from the intersecting columns, which frequently uncovers naked singles or pointing pairs.
What is the difference between an X-Wing and a Swordfish?
An X-Wing is a 2-line fish (2 rows, 2 columns). A Swordfish is a 3-line fish (3 rows, 3 columns). The underlying logic is identical.
Related Solving Techniques
Expand your repertoire by learning prerequisites and advanced counterparts:
Ready to Practice X-Wing?
Try a puzzle in the Hard tier (Peak Score 51–60), or browse all 25 techniques.