Sudoku Solver

Extreme

Jellyfish (Row)

A 4x4 pattern where a candidate appears in only four rows, restricted to the same four columns.

Jellyfish (Row) is the horizontal version of the Jellyfish (Column) and the expanded version of the Swordfish (Row). It uses a massive 4x4 pattern involving four rows and four columns.

It proves that "since the numbers for these 4 rows MUST be in these 4 columns, no other cells in those columns can have that number."

Interactive Example

1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
6
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
4
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
7
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1
1 2 3 4 5 6 7 8 9
3
1 2 3 4 5 6 7 8 9
2
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
5
1 2 3 4 5 6 7 8 9
6
1 2 3 4 5 6 7 8 9
1
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
4
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
2
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
4
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
7
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
5
1 2 3 4 5 6 7 8 9
9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
6
1 2 3 4 5 6 7 8 9
1
1 2 3 4 5 6 7 8 9
5
1 2 3 4 5 6 7 8 9
4
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
5
1 2 3 4 5 6 7 8 9
7
1 2 3 4 5 6 7 8 9
2
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
6
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
2
1 2 3 4 5 6 7 8 9
6
1 2 3 4 5 6 7 8 9
8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
7
1 2 3 4 5 6 7 8 9

Click "Apply Logic" to see the strategy in action.

Real Example Walkthrough

In the example puzzle above, the strategy targets the number 3:

1. The Base Sets (Rows) We look at four specific rows: - Row 2 - Row 4 - Row 8 - Row 9

In these four rows, the candidate 3 appears only in four columns: - Column 1 - Column 6 - Column 8 - Column 9

2. The Pattern Let's map out where 3 can go in our base rows: - Row 2: Restricted to Cols 1, 9 - Row 4: Restricted to Cols 6, 9 - Row 8: Restricted to Cols 6, 8 - Row 9: Restricted to Cols 1, 8

3. The Logic - We need to place four 3s—one for Row 2, Row 4, Row 8, and Row 9. - We have exactly four columns available for them (Cols 1, 6, 8, 9). - Therefore, these four columns must contain the 3s for our four base rows. - Consequently, no other cell in Column 1, Column 6, Column 8, or Column 9 can contain a 3.

4. The Elimination We can eliminate 3 from any cell in the cover columns (1, 6, 8, 9) that is NOT part of our Jellyfish pattern. - Eliminate 3 from R1C9. - Eliminate 3 from R6C1. - Eliminate 3 from R6C6. - Eliminate 3 from R6C9.

How to Spot a Jellyfish (Row)

  1. Look for Rows with Few Candidates: Use candidate highlighting to find rows that have only 2, 3, or 4 of a specific number.
  2. Match 4 Rows: Find 4 such rows where the candidates all align into exactly 4 columns.
  3. Eliminate Vertically: Once found, eliminate that number from the rest of those columns.

Visual Guide

C1 C2 C3 C4 R1 X X . . <- Row 1 (Base) R2 . X X . <- Row 2 (Base) R3 . . X X <- Row 3 (Base) R4 X . . X <- Row 4 (Base) | | | | v v v v Eliminate from Cols

  • 4 Base Rows restrict candidates to 4 Cover Columns.
  • Eliminate candidates from the Cover Columns vertically.

Common Mistakes

  • Confusing Direction: A "Row" Jellyfish eliminates from "Columns". Don't get it backward!
  • Incomplete Set: Using 4 rows that spill into a 5th column invalidates the logic.

Comparison Table

Strategy Pattern Size Base Sets Cover Sets Elimination
X-Wing (Row) 2x2 2 Rows 2 Cols Clean vertical kill
Swordfish (Row) 3x3 3 Rows 3 Cols Clean vertical kill
Jellyfish (Row) 4x4 4 Rows 4 Cols Clean vertical kill

Related Strategies