Help with X-wings

Advanced methods and approaches for solving Sudoku puzzles

Help with X-wings

Postby sususudoku » Sat Jun 03, 2006 6:12 am

I've read a LOT of X-wing explanations and haven't understood ANY of them. Could anyone please direct me to a CLEAR, UNAMBIGUOUS one? I guess I'd classify myself as a "high intermediate" but I need something written so ANYONE can understand it!

Thanks!
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Postby doduff » Sat Jun 03, 2006 6:50 am

Here is a picture of an X-Wing:

Image

The red lines connect 2's that are strongly linked... they are the only possibilities for 2 in rows 4 and 8. The possible ways that those two can be in the solution are marked, one in red and the other in blue(2's written in blue cells). Both possibilities lead to the elimination of the Twos in the red boxes marked with a red X's.

This can be extended to more than 2 rows(or columns). Here is a Swordfish, which is the same concept only has more cells.

Swordfish:

Image

In the picture above, the possibilities are again marked with read and blue 2's. and the 2's in the boxes marked with red X's can be eliminated.

Basically you find possible cells for a particular number in a row (or column )and you have to find the same possible cells(some can be filled with other numbers) in more rows(or columns) and then you eliminate what ever line up with those cells along the columns(or rows)-notice the switch here.

These concepts can be extended to 4 or more rows/columns and they call the squirmbags or squirmfishes or octopi or something... 'higher fishes'. I think there are example of x-cycles.

I hope that helps.
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Re: Help with X-wings

Postby Cec » Sat Jun 03, 2006 7:10 am

sususudoku wrote:"..I've read a LOT of X-wing explanations and haven't understood ANY of them......but I need something written so ANYONE can understand it!..."

I've seen many explanations of the "X-wing" pattern but I found emm's following explanation was the easiest to understand:

"XWING : If there are only two candidates of a number in any 2 rows (or columns) and they are also in exactly the same 2 columns (or rows) then they form an Xwing and you can eliminate that candidate elsewhere in those columns (or rows)."

For further details of emm's related post just click on Here

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Postby Havard » Sat Jun 03, 2006 11:41 am

I wrote this a while back: http://forum.enjoysudoku.com/viewtopic.php?t=3326

Maybe that can help you.

Havard
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Postby sususudoku » Fri Jun 09, 2006 6:05 am

Thank you all for responding. Problem finally solved!

Me
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Help with X-wings

Postby Cec » Sat Jun 10, 2006 9:35 am

Havard wrote:I wrote this a while back: http://forum.enjoysudoku.com/viewtopic.php?t=3326
Maybe that can help you.

Excellent. A "no frills" easy to understand presentation - previous accolades says it all.

Cec
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