As you continue learning more about the game of Sudoku, you’ll find that there is more to this simple yet addicting game than meets the eye. It's not just some rectangle or square that old people like to solve on a Friday night. There are many terms and mechanics to learn and master to make the most of each of the nine cells in every subgrid or box, and there are more than a handful of useful techniques to choose from that can make solving a Sudoku puzzle a lot easier.

One of these techniques is called the Swordfish strategy—a very useful tool to use when it comes to eliminating several number candidates at once. This technique is best learned after getting the hang of the basics, like Scanning, Intersections and Pencil Marking. If you haven't tackled these topics yet or have trouble handling only two cells, then we highly suggest you focus on learning them first or check out our guides on these subjects here on our blog.

Why is it named Swordfish? Is it an easy Sudoku trick to learn? And how does it form and take effect? We'll cover these as you continue reading more Sudoku tips and improve your puzzle knowledge with the info below!

What Is the Sudoku Swordfish?

Origin

The Swordfish strategy or Swordfish technique is an intermediate technique that is similar to the logic of how X-Wings work— but involves more other cells. There are no concrete records on why it’s called Swordfish and how it was created, but there are a lot of techniques in the Sudoku world that are named after marine animals that are not truly explained. Some hardcore Sudoku players think it originated from the Sudoku programmer forums back in the 2000s, but there is no legitimate proof of this.

While it's true that the other parts of the Sudoku puzzle are named normally, like rows and columns, or technically, like locked subsets and naked pairs, several of the more advanced techniques like these are named with the sea in mind, like Swordfish and Jellyfish. So it would not be uncommon to see more fish-themed moves developed for Sudoku at some point in the future.

Getting Started

As with most Sudoku tricks, you need to fill in rows and columns of the grid with enough candidate digits before identifying which cells you’ll use for the Swordfish pattern. Once you're done placing the temporary values, you can now look for a repeating candidate number among the cells. Let’s use this example:

You’ll be able to notice that we have the candidate number 4 repeating in cells r1c4, r1c8, r5c2, r5c4, r9c2 and r9c8. What does r1c4 mean? It means row 1, column 4 (r1c4). For more information on common terminologies, use this link. If you're still not familiar with how these terms work, it's best to pause this article here and go back to the basics before you tackle this technique.

And there’s another aspect you’ll observe as you learn the Sudoku Swordfish in this example—the candidate 4 repeats in three columns and three rows. These are the most important parts of this technique. You’ll need to have a repeating candidate in three rows and columns. The Sudoku Swordfish pattern is here in these pairs.

What Can the Swordfish Pattern Do?

Conditional Strength

The Sudoku Swordfish strategy works as a strong opening technique for advanced to hard Sudoku puzzles as it can effectively eliminate candidates in one go, given that certain conditions are met. Successfully applying the technique will present you with a better position in solving the puzzle. This can both save time and effort, especially with harder grids.

In our example, there are six cells with the repeating candidate 4 and they fall within the three rows and three columns condition. Take note of the positions carefully.

New players might have a lot of difficulty understanding this technique, but it is a crucial technique to learn to improve how you eliminate candidates in Sudoku puzzles. So we'll try to explain it as clearly as we can. You can also take notes from other experienced players you interact with as well.

Using the Sudoku Swordfish Strategy

Confirming the Process

Now, we begin using the Swordfish pattern. Let’s start looking at row 1, specifically, r1c8. We'll start using this solving technique from here and go from end to end of the Swordfish.

If we start here and choose this as our first correct cell, then we remove the candidate digit 4 in cell r9c8 as there can be no repetitions in the same column. Then we move to the next end of the Swordfish that was next to r9c8, which is r9c2 in the same row. Since r9c8 is removed, then r9c2 must be correct.

Then the nearest one is r5c2, which is eliminated since the previous one was deemed correct. After that, r5c4 of the same row is considered correct since the previous one is eliminated. And lastly, r1c4 is eliminated since the last candidate was chosen to be correct.

We are now left with three candidates, the 4s that are considered to be true. So by the rules of the game, we can now eliminate the other candidate 4s that are in the cells of the same three columns.

Completing the Swordfish

Congratulations! You’ve done the Sudoku Swordfish strategy and eliminated candidates in more than three cells! Once you understand it more, you can significantly lower the difficulty of your Sudoku puzzles and fill in the grid with more confidence behind the numbers you press or write. You can progress your skill and familiarity by testing out the Sudoku Swordfish with different puzzles and examples. Just don't forget to take a break and don't force yourself to learn the theory behind it in one go.

The Swordfish and Its Synergy With Other Sudoku Techniques

Since the Swordfish is a highly efficient candidate eliminator, it’s best used during the beginning stages of the game to remove as many numbers as possible. Think of it as using one of your more aggressive moves in an opening play or starting strong in the early stages. To chain it with the Wings, like X-Wing or Y-Wing, can make even the most daunting puzzle easier to handle.

However, keep in mind that Swordfish has to meet certain conditions to work, and not every puzzle can be effectively solved by it, so it is limited by that. If you're not confident in using the Swordfish in a solution just yet, try it out on easy puzzles right here on our site, sudokuconquest.com.

Don't be afraid to try to test out new skills on easier or even basic difficulties, especially if you're still in the early stages of learning Sudoku as a whole. If you feel that you'd learn it better as a sheet puzzle you can touch, then feel free to download and print easy sheets as much as you need.

Further Tips for Sudoku Puzzles

Once you’ve used the Sudoku Swordfish, it can pave the way for you to be able to use your other moves, such as the X- or Y-Wing, to whittle down even more of the pencil-marked number candidates. But remember, all these techniques are only as effective as the player that uses them. With proper usage, they can pull you out of a tight corner when you're having problems solving the puzzle.

Aside from learning pattern-based techniques, it's also important to keep your basic skills sharp. Scanning and Pencil Marking are more vital than even these techniques—after all, if your initial scan and candidate placements are incorrect, then it won't matter if you execute the techniques correctly, the results will still be wrong.

They’re not cheat codes, but rather, tools that can help you solve the game more efficiently. Keep that in mind, choose your candidates wisely, take your time in playing and you’ll become a better Sudoku player in no time!

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