The "ソードフィッシュ" is an advanced 数独 strategy, typically used in difficult levels of 数独 puzzles to eliminate candidates. The "ソードフィッシュ" method is similar to the "X-Wing," but it uses three sets of cells instead of two.
To understand it better, let's look at an example.
6 is our "fish digit," and rows 1, 6, and 9 are the base sets. The candidate cells for the number 6 also align perfectly in 3 columns. Because of this, there are two possible options for where the number 6 can be placed.
Either here:
Or here:
Regardless of which placement is correct, the three base sets (the rows) cover the three columns, meaning the number 6 cannot appear twice in any of them. したがって, we can safely eliminate the candidate 6 from all other メモ in these columns.
Now you know how to apply the "ソードフィッシュ" method in 数独. It can be difficult to spot, but it is a very useful addition to your 数独-solving arsenal.