Swordfish Sudoku Strategy

How the strategy works

A Swordfish pattern happens when one candidate is restricted to the same three columns across three rows. That candidate can be removed from other cells in those columns.

Because the pattern is easy to overread, it should come after singles, pairs, and X-Wing.

Large print practice routine

Use this technique slowly on a readable board or a printed sheet. The goal is to remove uncertainty, not to solve faster.

After each candidate cleanup, return to scanning and singles before looking for another advanced pattern.

Swordfish belongs near the end of a hard solve. For large print players, it is usually more comfortable on a printed sheet where rows and columns can be marked lightly without shrinking the board. Treat it as an advanced cleanup pass, not a routine first scan.

• Pick one candidate number.
• Scan three rows that each have two or three positions for that candidate.
• Confirm the positions use the same three columns.
• Remove the candidate from other cells in those columns.

Example pattern

Example: candidate 9 appears only in columns 1, 5, and 8 across three different rows. If those rows collectively lock 9 into the same three columns, the 9s for those rows must occupy those columns.

Other 9 candidates in columns 1, 5, and 8 can then be removed outside the three locked rows. The value is not placed yet; the board is cleaned so simpler moves can return.

Common mistakes to avoid

Do not look for Swordfish before singles, pairs, and X-Wing have slowed down. Advanced pattern hunting too early makes the board harder to read.

Do not accept a loose three-row pattern unless all candidate positions stay inside the same three columns. Extra positions break the logic.