ARTICLE

Swordfish Technique: Complete 3x3 Grid Pattern Guide

Master the Swordfish strategy in Sudoku with a full 9x9 visual diagram. Learn how a 3x3 candidate matrix across three rows and three columns eliminates candidates.

Once you have mastered the 2×2 X-Wing pattern, the next major weapon in your arsenal is Swordfish. While X-Wing locks a candidate digit across 2 rows and 2 columns, Swordfish expands the exact same logic to a 3×3 grid across 3 rows and 3 columns.

1. How Swordfish Works (3 Rows × 3 Columns)

Focus on a single digit (for example, digit 4):

In three different rows (Base Set), the possible cells for digit 4 appear ONLY within the exact same three columns (Cover Set).
Each of those three rows does not need to have all 3 cells filled—having just 2 or 3 candidate cells per row inside those three columns is sufficient!
Because the 3 rows must place three 4s in total, those three columns are completely claimed by the Swordfish rows. Any other candidate 4 in those three columns can be eliminated.

2. 9×9 Visual Diagram of a Swordfish (Digit 4)

In the diagram below, look at Rows 2, 5, and 8. Candidate 4 only appears in Columns 1, 5, and 9 (green cells). Notice that each row only has 2 candidates forming a closed loop across the 3 columns:

4✕	.	.	.	4✕	.	.	.	.
4	―	―	―	4	―	―	―	―
.	.	.	.	.	.	.	.	4✕
4✕	.	.	.	.	.	.	.	.
―	―	―	―	4	―	―	―	4
.	.	.	.	4✕	.	.	.	.
.	.	.	.	.	.	.	.	4✕
4	―	―	―	―	―	―	―	4
.	.	.	.	.	.	.	.	.

Result: All red dashed cells (`4✕`) in Columns 1, 5, and 9 outside of Rows 2, 5, and 8 can have candidate 4 eliminated!

Back to Home