Swordfish

Level: first needed in Extreme puzzles. In one line: An X-Wing with three rows and three columns.

A Swordfish is an X-Wing stretched to three rows and three columns. If, in three rows, a number can only go in cells that lie in the same three columns (two or three cells per row), then the three copies of the number in those rows will fill those three columns.

So each of the three columns already has its copy inside the pattern, and the number can be removed from every other cell of those columns. As always, rows and columns can be swapped.

Example from a real puzzle

This position comes from an Extreme puzzle in Sudoku Arena, at the exact moment the Swordfish is the next logical move. Cells are named by row and column: R3C4 means row 3, column 4.

Cells that form the patternCandidate you can remove

Swordfish on 1 across rows 2, 5, 9. Result: remove 1 from R7C8.

Play this puzzle and look for the move yourself. It's a practice game, so it doesn't count towards your stats.

How to spot it

  1. Choose a number and note its possible places in every row.
  2. Find three rows where all of its places fall within the same three columns.
  3. Remove the number from the rest of those three columns.

Tips

  • Not every row needs three cells; patterns of 2-2-2, 2-2-3 and so on all work.
  • Swordfish is rare. Look for it only after singles, pairs and X-Wings are exhausted.

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