Swordfish
The three-row extension of X-Wing — three rows with a digit in 2–3 cells, all confined to three columns.
What is Swordfish?
Swordfish is the three-row (or three-column) generalization of the X-Wing technique, and it represents a major leap in pattern complexity. It occurs when a digit appears as a candidate in exactly 2 or 3 cells in each of three rows, and all of those cells together are confined to the same three columns (no candidate appears in a fourth column). The logic mirrors X-Wing: since the digit must appear exactly once in each of the three rows, and all candidate cells are within three columns, the three columns will each receive exactly one instance of the digit from these three rows. This locks out the digit from any other cell in those three columns, enabling powerful eliminations. The difficulty with Swordfish is that the three rows do not each need to have candidates in all three columns — a row might have candidates in only two of the three columns, as long as across all three rows, no candidate falls outside the designated three columns. This flexibility makes Swordfish patterns more varied and harder to spot than X-Wing.
When to Use Swordfish
Apply Swordfish after X-Wing when further column or row eliminations are needed and simpler techniques are exhausted. Look for a digit that has exactly 2 or 3 candidate positions in at least three rows, where those positions share only three columns across all three rows. Swordfish is rare in Easy and Medium puzzles but appears regularly in Hard and Expert grids. An efficient search strategy: build a candidate frequency table for each digit, listing rows with 2–3 candidates and their column positions. If you find three rows where the union of column positions contains exactly 3 columns, you have a Swordfish candidate — verify and apply.
How to Apply Swordfish — Step by Step
- 1
Select a digit and list qualifying rows
Choose a digit and identify all rows where it appears in exactly 2 or 3 candidate cells. Rows with 4 or more candidate positions for that digit cannot be part of a Swordfish. Make a table showing each qualifying row and the column positions of its candidates.
- 2
Find three rows with a shared column set
From your list, look for any three rows where the union of all candidate column positions contains exactly 3 distinct columns. For example, Row 1 has candidates in columns {2, 5}, Row 4 has candidates in columns {2, 7}, and Row 8 has candidates in columns {5, 7} — the union {2, 5, 7} contains exactly 3 columns, forming a Swordfish pattern.
- 3
Verify strict confinement
Confirm that across all three rows combined, the digit's candidates appear exclusively in the three identified columns. No candidate cell for this digit in any of the three rows should lie outside those three columns. If a candidate in any row appears in a fourth column, the Swordfish is invalid for those rows.
- 4
Eliminate from the three columns
Since the digit must appear in each of the three rows and all placements are within the three columns, the digit is locked out of any other row in those columns. Remove the digit as a candidate from all cells in Columns 2, 5, and 7 (in the example) that are not part of the Swordfish rows (Rows 1, 4, 8). Rescan the board afterward for triggered patterns.
💡 Pro Tip
Swordfish can be validated by checking if the 3 rows × 3 columns intersection contains exactly the required cells. Use a candidate grid for clarity. A key mental model: think of Swordfish as "X-Wing with one extra row." If you've already found an X-Wing but it doesn't produce useful eliminations (because the cells in the columns outside the X-Wing don't have that digit as a candidate), look for a third row that fits the same column set — you may have a Swordfish that does produce eliminations. Also, always check the column-first variant: three columns with the digit confined to three rows, eliminating from those rows.
Practice Swordfish Now
Put this technique to the test on a live puzzle. The Practice Mode lets you work through real examples with candidate marking.