What is swordfish in sudoku

In this article I will use one of my handcrafted Sudoku puzzles that has a known Swordfish pattern. Download this very hard Sudoku puzzle 2 if you wish to try to solve this puzzle yourself.

You will need to partially solve the puzzle to reach the pattern as shown in the picture below. You will encounter naked and hidden singles, naked pairs, and locked candidates.

You will also need to solve some cells using the colors technique. Read my article "Solve Sudoku" for a step by step description on how to reach the place where you apply this technique. Some of these terms except locked candidates and color are explained in my illustrative article Sudoku Tips. Sudoku Swordfish is a variation of the X-Wing pattern. A Swordfish pattern occurs when three rows or three columns each contain 2 or 3 cells that hold a matching locked candidate.

This candidate must reside in each of the three rows and share the same three columns or vice versa. In the example above, the rows of the green squares contain at least two and no more than three 8s, but two of the columns contain other 8s. In a swordfish where the rows contain no more than three of a candidate, the columns can contain more than three. When this is the case as in the example image , you can eliminate any candidates on the columns except for the ones that form the swordfish.

In this case, there are 8s in the red squares. The 8s are highlighted yellow. These yellow 8s can be eliminated. Even if you know it's there, it can take some time to find.

But, in the interest of being complete, I will cover it. Take a look at this example: The puzzle above has a Swordfish on the number 5. There are three rows where all the possible 5s appear in the same three columns. Here is the same puzzle, but with some markings added for illustration: As you can see, the three rows marked by the blue lines all have their possible locations for a 5 confined to the same three columns marked by the red lines.

I've done so now and re-worded the paragraph. Very glad you are enjoying the site! Wednesday Feb I reduced the diagram to a simpler state to illustrate the pattern but I can see that could be confusing. I'd taken off the bottom two rows and only put in sufficient Xs to show one pattern but on its own, yes, other sword fishes are possible. So I have now replaced the old diagram with a full one.

Refresh the page. Wednesday 5-Dec Does a or combination also work? Thursday Feb The simplest formation in Example 1 is "A locked set of 3 locked-pairs sharing the same 3 rows and same 3 columns ". Monday Dec This was caused due to the fact that a swordfish is an X-Cycle as well.

I would like to suggest that this topic starts of with the Swordfish to fully explain this subject and then focus on , , etc.

Friday 2-Dec This shows 3 parallel lines that show some similarity with a Swordfish. Proof: - If cell B would contain numer 5, then cells B and D cannot contain 5. Therefore, on row F, cell C must contain a 5 single candidate , and at row J, cell F must contain a 5 again: single candidate.

Since number 5 must be in cell C or E on column 2, cell X cannot contain number 5. In column 5 cell A or F must contain number 5, and at column 9 cell B or D must contain number 5. Number 5 can thus be removed from all other cells at these columns. These locked pairs are not valuable for the Swordfish strategy, but in my opinion these locked pairs represent the Swordfish pattern and gave name to this strategy. Monday 4-Jul Are there clues to "find' the Swordfish number?

Is there some significance for this? I see the usefullness of this technique but spotting the correct number is difficult. Easiest way it to highlight the each number in the solver and see if you can spot a pattern in rows or columns.

You'll also be looking for 2x2 X-Wing and you should use those first. So you're looking for the minimum number of X in one dimension and an excess of X in the other.

Wednesday Apr I've got new ideas for me from this site. But you would have more simple methods, and then last example would disappear, such as "Perfect Swordfish".

You have many hard strategies but you have little simple methods.