Swordfish
What's a Swordfish?
A swordfish is like a bigger, fancier version of an X-wing. Instead of a candidate number being limited to just two rows and columns, a swordfish involves three rows and three columns (or three columns and three rows). If in those three rows the candidate appears in only three columns, you've found a swordfish pattern.
The logic: since each of the three rows must contain the candidate, and it can only appear in those three shared columns, that digit will definitely occupy one cell in each row within those columns. This allows you to eliminate the candidate from other cells in those same columns.
This is a natural progression from X-Wing and builds on the foundation of naked singles and hidden singles.
Why is it called "Swordfish"?
It's called "Swordfish" because of how the pattern looks when you mark it out on the Sudoku grid. The three rows and three columns form a crisscrossing pattern that sort of resembles the long body and pointed bill of a swordfish.
Sudoku names like X-Wing, Swordfish, and Jellyfish all come from these "fishy" shapes that show up when candidates line up across rows and columns. The bigger the fish, the more rows and columns are involved.
Why It Matters
Swordfish is often a mid-to-advanced technique. It's rarer than X-wings, but when it shows up, it can break a deadlock in harder puzzles. It's essentially a "three-pronged" extension of the X-wing, letting you cut away stubborn candidates in bulk.
Step-by-Step: How to Spot a Swordfish
- Pick a candidate digit (say "4").
- Scan rows (or columns) for that candidate.
- Find three different rows where that digit appears as a candidate in only three columns.
- Check alignment — the candidates must all fall within the same three columns.
- If the pattern holds, you've built a swordfish.
- Eliminate that candidate from all other cells in those columns outside the pattern rows.
Example Walkthrough
Imagine the digit "7":
- Row 2 has candidates {c3, c5, c7}
- Row 5 has candidates {c3, c5, c7}
- Row 8 has candidates {c3, c5, c7}
This is a textbook swordfish. Because each row must contain one 7, and only in columns 3, 5, and 7, you can now eliminate 7 from every other cell in columns 3, 5, and 7 outside those three rows.
Common Pitfalls
- False positives: not every three-by-three grid of candidates is a swordfish. You need the exact overlap across rows and columns.
- Forgetting symmetry: swordfish works both ways — rows defining columns, or columns defining rows.
- Overcomplicating it: keep the logic simple. Think: "three rows, three columns, overlap matches, eliminate elsewhere."
Variations You Might Meet
- Finned swordfish: if an extra candidate (a "fin") sticks out from the tidy 3×3 structure, you can still use swordfish logic but must test both possibilities carefully.
- Sashimi swordfish: a distorted version where one row/column has only two candidates instead of three, but elimination still works with careful checking.
Both are powerful next‑level moves once you're comfy spotting classic X‑wings.
Why Swordfish Feels Satisfying
Catching a swordfish feels like unlocking a hidden pattern. You've spotted structure in chaos, and suddenly whole swaths of candidates vanish. It's one of those strategies that separates casual solvers from players who really "see" the logic of Sudoku.
Practice Tips
- Start by scanning for X-wings; swordfish often pop up when you notice an "almost X-wing" that stretches across three rows.
- Highlight candidate positions on paper or digitally — patterns jump out faster when marked.
- Don't overhunt; swordfish are less common, so trust the puzzle flow and check when you're stuck.
Wrap-Up
Swordfish is the natural extension of the X-wing — bigger, rarer, and more powerful. Once you learn to recognize it, you'll have another reliable tool in your solving arsenal for those tougher puzzles that refuse to crack.
Ready to advance? Check out our complete strategy guide for more techniques like XY-Wing and Trial & Error.
Frequently Asked Questions
What's a Swordfish in Sudoku?
A swordfish is like a bigger, fancier version of an X-wing. Instead of a candidate number being limited to just two rows and columns, a swordfish involves three rows and three columns (or three columns and three rows). If in those three rows the candidate appears in only three columns, you've found a swordfish pattern.
How do I spot a Swordfish pattern?
To spot a Swordfish: 1) Pick a candidate digit (say "4"), 2) Scan rows (or columns) for that candidate, 3) Find three different rows where that digit appears as a candidate in only three columns, 4) Check alignment — the candidates must all fall within the same three columns, 5) If the pattern holds, you've built a swordfish.
What's the difference between Swordfish and X-Wing?
X-Wing involves two rows and two columns, while Swordfish extends this to three rows and three columns. Swordfish is essentially a "three-pronged" extension of the X-wing pattern, letting you eliminate stubborn candidates in bulk. It's rarer than X-wings but more powerful when it appears.
When should I look for Swordfish patterns?
Look for Swordfish patterns when you're stuck and basic techniques aren't working. Start by scanning for X-wings — swordfish often pop up when you notice an "almost X-wing" that stretches across three rows. Don't overhunt for them as they're less common than other techniques.
What are the variations of Swordfish?
Variations include: 1) Finned swordfish - if an extra candidate (a "fin") sticks out from the tidy 3×3 structure, you can still use swordfish logic but must test both possibilities carefully, 2) Sashimi swordfish - a distorted version where one row/column has only two candidates instead of three, but elimination still works with careful checking.
Practice Swordfish
Feeling stuck? Sometimes even experts need Trial & Error.