The Swordfish
The Swordfish is the X-Wing with a third line. A digit, in three columns, fits only in the same three rows. Those rows get their copies from those columns, so the rest of each row loses the digit.
Ninesmith Sudoku ·
In short
- In three columns, a digit fits only within the same three rows (or the other way round).
- Each column needn't use all three rows: two places each is enough.
- Strike the digit from the rest of those three rows.
An example
No two of these columns make an X-Wing on their own: each pair of them spans three rows. Only all three together close the set. That is why the Swordfish is hard to see, and why it's worth knowing.
How to find one
- Look at one digit alone, with complete notes.
- List the columns where it has two or three places, and the rows those places are in.
- Look for three columns whose places fit inside three rows. Then do the same with rows.
- Check that the three cross lines have the digit somewhere else to strike.
Why it works
The three columns need three copies of the digit, in three different rows, and they only have rows 4, 5 and 6 to use. So rows 4, 5 and 6 each get their copy from these columns, and no other cell in those rows can have it.
Questions
What is a Swordfish in Sudoku?
A pattern where a digit, in three rows, fits only in the same three columns (or the reverse). The digit can then be removed from the rest of those three columns.
Is a Swordfish harder than an X-Wing?
It is harder to spot, because the shape isn't a clean rectangle. The logic is the same, with three lines instead of two.
Next: Y-Wing · all techniques
Drill the Swordfish with the Smith
Ninesmith Sudoku is a calm Sudoku app for iPhone. Its Pattern Trainer drills the Swordfish in sessions of 30 to 90 seconds, and in your own puzzles the Smith names the technique and shows the pattern before anything goes in.
Get the appThe full Swordfish drills are part of Premium; the first scenario is free. No ads in any tier.