Jellyfish

Level 8 · Blue Belt

Strategy:

Requires:

Learn after:

Finned Jellyfish Franken Jellyfish Squirmbag

Overview

Jellyfish is the four-row, four-column extension of fish patterns. When a candidate in four rows is restricted to the same four columns, it can be eliminated from other cells in those columns.

How It Works

Find four rows where a candidate appears, with all occurrences in the same four columns.
Each row must have 2-4 occurrences of the candidate within these columns.
Eliminate the candidate from other cells in those four columns.

Example

Look for Jellyfish.

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

1

Jellyfish

Check digit 2 in columns 1, 2, 5 and 8.

Sudoku grid illustrating step 1: Jellyfish — Check digit 2 in columns 1, 2, 5 and 8.

2

Jellyfish

r3c1 is already filled with 4.

Sudoku grid illustrating step 2: Jellyfish — r3c1 is already filled with 4.

3

Jellyfish

r5c1 is already filled with 3.

Sudoku grid illustrating step 3: Jellyfish — r5c1 is already filled with 3.

4

Jellyfish

r7c1 is already filled with 5.

Sudoku grid illustrating step 4: Jellyfish — r7c1 is already filled with 5.

5

Jellyfish

Digit 2 cannot go in r8c1 because r8c3 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 5: Jellyfish — Digit 2 cannot go in r8c1 because r8c3 is already in this row. Remove the entry or choose a different digit.

6

Jellyfish

r9c1 is already filled with 8.

Sudoku grid illustrating step 6: Jellyfish — r9c1 is already filled with 8.

7

Jellyfish

r3c2 is already filled with 3.

Sudoku grid illustrating step 7: Jellyfish — r3c2 is already filled with 3.

8

Jellyfish

r5c2 is already filled with 6.

Sudoku grid illustrating step 8: Jellyfish — r5c2 is already filled with 6.

9

Jellyfish

r7c2 is already filled with 1.

Sudoku grid illustrating step 9: Jellyfish — r7c2 is already filled with 1.

10

Jellyfish

Digit 2 cannot go in r8c2 because r8c3 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 10: Jellyfish — Digit 2 cannot go in r8c2 because r8c3 is already in this row. Remove the entry or choose a different digit.

11

Jellyfish

r9c2 is already filled with 4.

Sudoku grid illustrating step 11: Jellyfish — r9c2 is already filled with 4.

12

Jellyfish

r3c5 is already filled with 9.

Sudoku grid illustrating step 12: Jellyfish — r3c5 is already filled with 9.

13

Jellyfish

r5c5 is already filled with 1.

Sudoku grid illustrating step 13: Jellyfish — r5c5 is already filled with 1.

14

Jellyfish

r7c5 is already filled with 4.

Sudoku grid illustrating step 14: Jellyfish — r7c5 is already filled with 4.

15

Jellyfish

Digit 2 cannot go in r8c5 because r8c3 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 15: Jellyfish — Digit 2 cannot go in r8c5 because r8c3 is already in this row. Remove the entry or choose a different digit.

16

Jellyfish

r9c5 is already filled with 7.

Sudoku grid illustrating step 16: Jellyfish — r9c5 is already filled with 7.

17

Jellyfish

r3c8 is already filled with 1.

Sudoku grid illustrating step 17: Jellyfish — r3c8 is already filled with 1.

18

Jellyfish

r5c8 is already filled with 5.

Sudoku grid illustrating step 18: Jellyfish — r5c8 is already filled with 5.

19

Jellyfish

r7c8 is already filled with 9.

Sudoku grid illustrating step 19: Jellyfish — r7c8 is already filled with 9.

20

Jellyfish

r8c8 is already filled with 4.

Sudoku grid illustrating step 20: Jellyfish — r8c8 is already filled with 4.

21

Jellyfish

r9c8 is already filled with 6.

Sudoku grid illustrating step 21: Jellyfish — r9c8 is already filled with 6.

22

Jellyfish

In each of these 4 columns, digit 2 is restricted to the same 4 rows: 1, 2, 4 and 6.

Sudoku grid illustrating step 22: Jellyfish — In each of these 4 columns, digit 2 is restricted to the same 4 rows: 1, 2, 4 and 6.

23

Jellyfish

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

Sudoku grid illustrating step 23: Jellyfish — That creates a Jellyfish: those rows must contain the digit for these columns, so other columns cannot keep it there.

24

Jellyfish

These are the extra 2 candidates in rows 1, 2, 4 and 6 that must be removed: r1c4, r2c6, r4c6, r4c9, r6c4 and r6c9.

Sudoku grid illustrating step 24: Jellyfish — These are the extra 2 candidates in rows 1, 2, 4 and 6 that must be removed: r1c4, r2c6, r4c6, r4c9, r6c4 and r6c9.

25

Jellyfish

Remove 2 from the extra cells in rows 1, 2, 4 and 6: r1c4, r2c6, r4c6, r4c9, r6c4 and r6c9.

Sudoku grid illustrating step 25: Jellyfish — Remove 2 from the extra cells in rows 1, 2, 4 and 6: r1c4, r2c6, r4c6, r4c9, r6c4 and r6c9.

26

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Jellyfish are quite rare - master X-Wing and Swordfish first.
Computer assistance is helpful for finding Jellyfish reliably.
The pattern may not use all 16 intersection cells.