Swordfish

X-Wing's bigger brother. Harder to see, but the logic is the same.

What is a Swordfish?

Pick one number. Find three rows where that number has only two or three possible cells, and where all of those cells fall into the same three columns.

The three rows need three of that number, and they can only place them in those three columns, one per column. So the three columns are covered, and the number can be removed from every other cell in them.

the swordfish cells its rows and columns candidates you can remove blue numbers: already filled in with the basics

Example from a real puzuru puzzle. Rows and columns are numbered 1 to 9 from the top left.

The example

The diagram shows only the candidates for 7. In rows 3, 5 and 9, every possible place for 7 lies in columns 4, 5 and 8.

Note that no single row uses all three columns. That is normal for a Swordfish: each row may have just two of the three.

Those three rows will fill the 7 for all three columns. Remove 7 from R6C5, R6C8, R7C4, R8C8.

How to find a Swordfish

Work one number at a time. List the rows where it has two or three candidates, with their columns.

Look for three rows whose columns, taken together, are only three different columns. Then check those columns for other candidates of the number.

At this point the puzzle has no X-Wing at all, in rows or columns, which is why the bigger pattern is needed.

Practice on Master puzzles →

← X-Wing　Next: XY-Wing →

FAQ

Is Swordfish harder than X-Wing?

It uses the same idea, but it's harder to see because it spreads over three rows and three columns.

Does each row need three candidates?

No. Each row can have two or three, as long as all of them fall into the same three columns.

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