‘Swordfish’ – An Advanced Sudoku Technique

The ‘Swordfish’ technique is designed for solving difficult Sudoku puzzles with many blank cells. This advanced technique helps eliminate potential candidate numbers and narrows down your choices. ‘Swordfish’ is similar to the ‘X-Wing’ technique but involves three rows and three columns instead of two. To effectively use this technique, you must identify three rows or columns that each have two occurrences of a specific candidate number.

Let’s consider an example. First, identify the ‘fish digit’ and the ‘base’ rows. In our first image, the ‘fish digit’ is number 5, and the base rows are 2, 6, and 8, highlighted by green guidelines. Each of these rows contains exactly two occurrences of the number 5. The columns containing the number 5 align perfectly with the rows are 2, 8, and 9, marked with red guidelines for clarity. With these conditions met—three rows and three columns—the ‘Swordfish’ pattern is established!

Now there are two ways to keep the number 5, either as shown in the second image or in the third image.

Next, you can keep all the fives in the green boxes and can eliminate all other candidate fives in the three columns involved, as shown in the fourth image where the candidates are crossed out in the red boxes. This significantly reduces the number of potential placements for the number 5 across the grid.

The Swordfish technique depends on the careful examination of rows and columns. Finding cells that need to be filled is one of the major challenges faced by players due to the numerous possibilities present. This method, although it is complicated, is very good at getting rid of irrelevant options thereby making the solving procedure easier. When you get adept with swordfish, you will be able to handle even the hardest Sudoku puzzles. Download our free printable Sudoku puzzle books and practice more.