Swordfish

The Swordfish is the X-Wing grown one size larger. Where an X-Wing works with two rows and two columns, a Swordfish uses three rows and three columns. It tracks a single digit, and when the pattern lines up it lets you sweep that digit out of three whole columns at once.

What is a Swordfish?

Pick a digit — say 4. Find three rows in which the 4 can go in only cells that fall within the same three columns. (Each row doesn't need the 4 in all three columns — two is enough, as long as no row strays outside the three.) Because the three 4s in those rows must occupy those three columns between them, the 4 is claimed there — and can be removed from every other cell in those three columns.

As with the X-Wing, the whole thing works with rows and columns swapped, too.

Step by step

1. Choose a digit and mark, row by row, which cells could still hold it.
2. Find three rows where that digit is confined to the same three columns.
3. Confirm the fish. No row may place the digit outside those three columns.
4. Eliminate the digit from every other cell in the three columns.
5. Re-scan. Then try the same with columns and rows reversed.

The fish family

Single-digit patterns come in a series by size: the X-Wing (2×2), the Swordfish (3×3), and the Jellyfish (4×4). The logic is identical each time — a digit confined to N lines across N cross-lines — just wider. Swordfish is the point where you really have to keep organised pencil marks to spot it.

Common mistakes

• A row that breaks out. If even one of the three rows can place the digit in a fourth column, it isn't a Swordfish.
• Expecting a full 3×3. Rows with the digit in only two of the three columns still count — that's normal.
• Eliminating in the rows. A row-based Swordfish clears the three columns, not the rows.

Which Sudoku types is this best for?

The same logic applies across variants, but it pays off more in some than others.