Variant Sudoku

Swordfish

When a digit’s spots in three rows all fall inside the same three columns, no other cell in those columns can have that digit.

Practice now
9
8
1
3
6
2
9
5
1
2
9
5
8
2
5
9
7
9
6
8
3
5
9
7
9
2
9
6
5
2
3
8
9
9
9
3
9
7
5
6
9
5
3
7
9
5
9
2
8
5
8
3
6
9
9
Clear 9 from the rest of the columns.

Why it works

On the board above:

In rows 1, 5 and 9, every spot for 9 sits in columns 2, 8 and 9.

Each of those three rows needs a 9, and no two can share a column. So together they put a 9 in all three columns.

That fills columns 2, 8 and 9. No other cell in them can be 9. Remove it from r6c2.

How to spot it

  1. Pick one digit

    Look only at its spots.

  2. Find rows with two or three spots

    Rows with more spots can’t be part of it.

  3. Look for three rows that use only three columns

    Not every row needs all three columns. Together they must use just three.

  4. Clear those columns

    Remove the digit from the other cells in the three columns.

Practice

Real boards from the solver, with every pencil mark filled in. Spot it, then use it, then find it cold.

Loading the boards…

Try it in a real puzzle

Each of these needs a Swordfish to finish. It opens in the player.

Tips

Check the X-Wing first

If two of the rows already make an X-Wing, use that. It is simpler.

Columns work too

Three columns whose spots use only three rows clear those rows.

Simple ColoringFollow one digit through houses where it has two spots, painting the spots in two colors. One color is true.Next: Simple Coloring →

In the glossary

Swordfish