Swordfish

Level 6 · Orange Belt (Green Stripe)

Strategy:

Requires:

Learn after:

Finned Swordfish Franken Swordfish Jellyfish

Overview

Swordfish extends X-Wing to three rows and three columns. When a candidate appears 2-3 times in each of three rows, and all occurrences fall within the same three columns, eliminations can be made.

How It Works

Find three rows where a candidate appears in at most 3 cells each, all within the same 3 columns.
The candidate must appear at least once in each row and column of the pattern.
Eliminate the candidate from other cells in those three columns.

Example

Look for Swordfish.

Sudoku grid showing the initial puzzle state for Look for Swordfish.

1

Swordfish

Check digit 3 in rows 2, 4 and 6.

Sudoku grid illustrating step 1: Swordfish — Check digit 3 in rows 2, 4 and 6.

2

Swordfish

r2c2 is already filled with 8.

Sudoku grid illustrating step 2: Swordfish — r2c2 is already filled with 8.

3

Swordfish

r2c3 is already filled with 5.

Sudoku grid illustrating step 3: Swordfish — r2c3 is already filled with 5.

4

Swordfish

r2c4 is already filled with 4.

Sudoku grid illustrating step 4: Swordfish — r2c4 is already filled with 4.

5

Swordfish

r2c5 is already filled with 6.

Sudoku grid illustrating step 5: Swordfish — r2c5 is already filled with 6.

6

Swordfish

r2c7 is already filled with 1.

Sudoku grid illustrating step 6: Swordfish — r2c7 is already filled with 1.

7

Swordfish

r2c9 is already filled with 9.

Sudoku grid illustrating step 7: Swordfish — r2c9 is already filled with 9.

8

Swordfish

r4c2 is already filled with 2.

Sudoku grid illustrating step 8: Swordfish — r4c2 is already filled with 2.

9

Swordfish

r4c3 is already filled with 4.

Sudoku grid illustrating step 9: Swordfish — r4c3 is already filled with 4.

10

Swordfish

r4c4 is already filled with 5.

Sudoku grid illustrating step 10: Swordfish — r4c4 is already filled with 5.

11

Swordfish

r4c5 is already filled with 9.

Sudoku grid illustrating step 11: Swordfish — r4c5 is already filled with 9.

12

Swordfish

r4c7 is already filled with 8.

Sudoku grid illustrating step 12: Swordfish — r4c7 is already filled with 8.

13

Swordfish

Digit 3 is not a current candidate in r4c9 because earlier solving steps already removed it.

Sudoku grid illustrating step 13: Swordfish — Digit 3 is not a current candidate in r4c9 because earlier solving steps already removed it.

14

Swordfish

r6c2 is already filled with 9.

Sudoku grid illustrating step 14: Swordfish — r6c2 is already filled with 9.

15

Swordfish

r6c3 is already filled with 8.

Sudoku grid illustrating step 15: Swordfish — r6c3 is already filled with 8.

16

Swordfish

Digit 3 is not a current candidate in r6c4 because earlier solving steps already removed it.

Sudoku grid illustrating step 16: Swordfish — Digit 3 is not a current candidate in r6c4 because earlier solving steps already removed it.

17

Swordfish

r6c5 is already filled with 4.

Sudoku grid illustrating step 17: Swordfish — r6c5 is already filled with 4.

18

Swordfish

r6c7 is already filled with 2.

Sudoku grid illustrating step 18: Swordfish — r6c7 is already filled with 2.

19

Swordfish

r6c9 is already filled with 5.

Sudoku grid illustrating step 19: Swordfish — r6c9 is already filled with 5.

20

Swordfish

In each of these 3 rows, digit 3 is restricted to the same 3 columns: 1, 6 and 8.

Sudoku grid illustrating step 20: Swordfish — In each of these 3 rows, digit 3 is restricted to the same 3 columns: 1, 6 and 8.

21

Swordfish

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

Sudoku grid illustrating step 21: Swordfish — That creates a Swordfish: those columns must contain the digit for these rows, so other rows cannot keep it there.

22

Swordfish

These are the extra 3 candidates in columns 1, 6 and 8 that must be removed: r5c1.

Sudoku grid illustrating step 22: Swordfish — These are the extra 3 candidates in columns 1, 6 and 8 that must be removed: r5c1.

23

Swordfish

Remove 3 from the extra cells in columns 1, 6 and 8: r5c1.

Sudoku grid illustrating step 23: Swordfish — Remove 3 from the extra cells in columns 1, 6 and 8: r5c1.

24

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Swordfish requires careful tracking of candidate positions.
Look for candidates that are restricted to few columns across multiple rows.
Pencilmark highlighting greatly helps in spotting this pattern.