Difficulty
Medium
Sudoku technique guide
X-Wing
Sometimes the obvious moves disappear, but the grid is still giving you a useful clue. X-Wing is a calm way to follow it.
By the end, you will know what to notice, how the idea works and when it is worth using.
At a glance
Technique family
Fish
Purpose
Removes candidates
Typical puzzle stage
Middle to late
Frequency
Occasional
Prerequisites
Strong links and candidate maps
Why this technique matters
X-Wing is the first fish pattern most solvers meet. It turns a repeated candidate position into a clear line-based elimination.
The idea in plain English
An X-Wing occurs when one digit has exactly two candidate positions in each of two rows, and those positions line up in the same two columns. The digit must occupy one position in each row, so it can be removed from other cells in those columns.
How to recognise it
Look for a single digit forming a two-by-two rectangle in candidate marks. The corners need not be adjacent.
Pause when you see this shape. You do not have to force it; just check whether the pattern is complete.
How the logic unfolds
Think of this as a short conversation with the grid. Take one check at a time, and let each answer tell you what to inspect next.
Start by. Choose one digit and scan its candidate positions row by row.
Then. Find two rows where that digit appears in exactly the same two columns.
Next. Treat the four corners as a rectangle.
Finally. Remove the digit from all other cells in those two columns.
Try X-Wing in the SudoSketch Learn Arena
When it usually appears
Use it when candidate work is established and simpler line or box techniques are no longer producing eliminations.
Common traps
These are easy places to get turned around. They are useful checks, not signs that you are doing badly.
- Using rows with three candidate positions. A basic X-Wing needs exactly two positions in each selected row.
- Removing candidates from the wrong columns or from the four corner cells.
Frequently asked questions
Can an X-Wing be based on columns?
Yes. Swap rows and columns; the logic is identical.
Does the rectangle have to be square?
No. It only needs the same two rows and the same two columns.
Quick takeaway
- A X-Wing belongs to the fish family.
- Its purpose is to remove candidates.
- Look for a complete pattern, not one that only nearly fits.
- It is most useful middle to late.
- Once you make the deduction, return to the simpler scans.