X-Wing in Sudoku
X-Wing is one of the first classic advanced fish patterns. It looks complex at first, but its logic is rigid: one digit forms a locked rectangle across two rows and two columns, which creates safe eliminations.
Summary
Find aligned two-row or two-column candidate patterns to eliminate values outside the pattern.
Table of Contents
What this technique is
X-Wing is a single-digit fish pattern where one candidate forms a locked rectangle across two rows and two columns.
When to use it
Use in hard/expert puzzles after notes are accurate and simpler elimination methods stop producing progress.
How it works
Track one candidate across rows or columns, confirm exact two-by-two alignment, then eliminate that candidate outside the four corner cells.
Step-by-step
- Choose one candidate digit.
- Find two rows (or columns) where that digit appears exactly twice.
- Confirm both rows share the same two columns (or vice versa).
- Eliminate that digit from other cells in those columns/rows.
Example
If candidate 5 appears in the same two columns in rows 2 and 7, other cells in those columns cannot contain 5.
Example
If candidate 5 appears exactly twice in row 2 and row 7 at the same two columns, other cells in those columns cannot contain 5 outside rows 2 and 7.
Diagram Placeholder
Use an example diagram section here to highlight the X-Wing corners and candidate removals for visual learning.
Common Mistakes
- Using rows/columns where a candidate appears more than twice.
- Eliminating from X-Wing corner cells themselves.
- Missing the column-first version of the same pattern.
- Tracking multiple digits at once instead of one digit.
- Forcing a pattern without exact alignment.
Practice Links
FAQ
What is X-Wing in Sudoku?
X-Wing is an advanced candidate elimination pattern based on aligned two-by-two positions.
Do I need notes for X-Wing?
Yes. Candidate notes are essential for identifying X-Wing patterns reliably.
Where does X-Wing appear most often?
It appears mostly in hard and expert Sudoku puzzles.