X-Wing

Level 4 · Yellow Belt (Orange Stripe)

Strategy:

Requires:

Locked Candidates

Learn after:

Crane Finned X-Wing Firework Franken X-Wing Simple Coloring Skyscraper Swordfish Two-String Kite

Overview

X-Wing is a fish pattern using two rows and two columns. When a candidate appears in exactly two cells in two different rows, and these four cells share the same two columns, the candidate can be eliminated from other cells in those columns.

How It Works

Find a candidate that appears in exactly two cells in a row.
Find another row where the same candidate appears in exactly two cells in the same columns.
These four cells form a rectangle. The candidate must be in two diagonal corners.
Eliminate the candidate from other cells in those two columns.

Example

Look for X-Wing.

Sudoku grid showing the initial puzzle state for Look for X-Wing.

1

X-Wing

Check digit 4 in rows 1 and 8.

Sudoku grid illustrating step 1: X-Wing — Check digit 4 in rows 1 and 8.

2

X-Wing

r1c2 is already filled with 6.

Sudoku grid illustrating step 2: X-Wing — r1c2 is already filled with 6.

3

X-Wing

r1c3 is already filled with 3.

Sudoku grid illustrating step 3: X-Wing — r1c3 is already filled with 3.

4

X-Wing

r1c4 is already filled with 5.

Sudoku grid illustrating step 4: X-Wing — r1c4 is already filled with 5.

5

X-Wing

r1c6 is already filled with 8.

Sudoku grid illustrating step 5: X-Wing — r1c6 is already filled with 8.

6

X-Wing

r1c7 is already filled with 2.

Sudoku grid illustrating step 6: X-Wing — r1c7 is already filled with 2.

7

X-Wing

r1c8 is already filled with 9.

Sudoku grid illustrating step 7: X-Wing — r1c8 is already filled with 9.

8

X-Wing

r1c9 is already filled with 7.

Sudoku grid illustrating step 8: X-Wing — r1c9 is already filled with 7.

9

X-Wing

r8c2 is already filled with 1.

Sudoku grid illustrating step 9: X-Wing — r8c2 is already filled with 1.

10

X-Wing

r8c3 is already filled with 5.

Sudoku grid illustrating step 10: X-Wing — r8c3 is already filled with 5.

11

X-Wing

r8c4 is already filled with 2.

Sudoku grid illustrating step 11: X-Wing — r8c4 is already filled with 2.

12

X-Wing

r8c6 is already filled with 3.

Sudoku grid illustrating step 12: X-Wing — r8c6 is already filled with 3.

13

X-Wing

r8c7 is already filled with 9.

Sudoku grid illustrating step 13: X-Wing — r8c7 is already filled with 9.

14

X-Wing

r8c8 is already filled with 7.

Sudoku grid illustrating step 14: X-Wing — r8c8 is already filled with 7.

15

X-Wing

r8c9 is already filled with 6.

Sudoku grid illustrating step 15: X-Wing — r8c9 is already filled with 6.

16

X-Wing

In each of these 2 rows, digit 4 is restricted to the same 2 columns: 1 and 5.

Sudoku grid illustrating step 16: X-Wing — In each of these 2 rows, digit 4 is restricted to the same 2 columns: 1 and 5.

17

X-Wing

That creates a X-Wing: those columns must contain the digit for these rows, so other rows cannot keep it there.

Sudoku grid illustrating step 17: X-Wing — That creates a X-Wing: those columns must contain the digit for these rows, so other rows cannot keep it there.

18

X-Wing

These are the extra 4 candidates in columns 1 and 5 that must be removed: r3c1, r9c1, r5c5 and r9c5.

Sudoku grid illustrating step 18: X-Wing — These are the extra 4 candidates in columns 1 and 5 that must be removed: r3c1, r9c1, r5c5 and r9c5.

19

X-Wing

Remove 4 from the extra cells in columns 1 and 5: r3c1, r9c1, r5c5 and r9c5.

Sudoku grid illustrating step 19: X-Wing — Remove 4 from the extra cells in columns 1 and 5: r3c1, r9c1, r5c5 and r9c5.

20

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

X-Wings work on rows (eliminating from columns) or columns (eliminating from rows).
Look for candidates with exactly 2 occurrences per row/column.
The pattern forms a rectangle - visualize the 'X' shape.