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Created page with "A '''Swordfish''' is a basic fish pattern with 3 rows and 3 columns. It is a single-digit solving technique. == Swordfish in the Rows == : When all can..."

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A '''Swordfish''' is a basic [[fish]] pattern with 3 [[row]]s and 3 [[column]]s. It is a [[single-digit]] [[solving technique]].

== Swordfish in the Rows ==

: When all [[candidate]]s for [[digit]] '''X''' in 3 rows are located in only 3 columns, we can [[eliminate]] all candidates for digit '''X''' from those 3 columns except those located on the defining 3 rows.

Here is a diagram that shows a Swordfish in the rows:

[[image:swordfish-rc.png|Maximum Swordfish in the rows]]

The candidates in the 3 defining rows are marked '''X'''. These candidates only occupy 3 columns. Because it is impossible to have more than one instance of a digit in a column, each instance of '''X''' in the defining rows must be placed in one of these 3 columns. In other words: the candidates for digit '''X''' in these 3 columns must be located in these 3 rows. This allows us to eliminate the remaining candidates in these 3 columns.

Each defining row can contain 2 or 3 candidates for digit '''X'''. A minimum Swordfish has a different appearance, but it still fits the definition:

[[image:swordfish-rc2.png|Minimum Swordfish in the rows]]

A minimum Swordfish can also be seen as a [[Fishy Cycle]].

=== Example ===

The diagrams are useful to understand how this technique works, but as you will see in the following example, a Swordfish is not easy to spot in a [[pencilmark]] grid.

[[image:swordfish-rcx.png|Minimum Swordfish in the rows example]]

Swordfish for digit '''9''' in rows 3,7,8 and columns 1,5,8.

== Swordfish in the Columns ==

: When all candidates for digit '''X''' in 3 columns are located in only 3 rows, we can eliminate all candidates for digit '''X''' from those 3 rows except those located on the defining 3 columns.

Here is the diagram for this version:

[[image:swordfish-cr.png|Swordfish in the columns]]

In this diagram, you can also see that is is possible to have 2 defining columns in a single [[chute]]. Two of the secondary lines can also be located in a single chute, but it is not possible to have 4 lines of a Swordfish crossing in a single [[box]]. In that case, the Swordfish would degenerate into a series of [[Locked Candidates]].

=== Example ===

Here is an example of a Swordfish in the columns:

[[image:swordfish-crx.png|Swordfish in the columns example]]

Minimum Swordfish for digit '''3''' in columns 1,5,7 and rows 1,5,7.

== Practice Sudokus ==

The following puzzles will help you practice this technique:
000308002000040700001970080905003006037000520800500903070096100006030000400807000
000000000008206900109804206004602500700000008001307400603405709005903800000000000
800060000000007600025900010008604000400000006000108300010006790002400000000090004
003105400000070000604903705501000302070030050802000907107306204000010000006207500
260907043730000089000000000100306005000070000400502001000000000340000097920403016
Select and copy each string and paste it into a computer program that accepts this input.

== See Also ==

* [[Fish]]
* [[X-Wing]]
* [[Jellyfish]]
* [[Finned Swordfish]]
* [[Sashimi Swordfish]]
* [[Franken Swordfish]]
* [[Mutant Swordfish]]

[[Category:Solving Techniques]]

Swordfish - Revision history

Rooted: Created page with "A '''Swordfish''' is a basic fish pattern with 3 rows and 3 columns. It is a single-digit solving technique. == Swordfish in the Rows == : When all can..."