And I hoped I understood X-Wings

Advanced methods and approaches for solving Sudoku puzzles

And I hoped I understood X-Wings

Postby georgers » Sat Jun 04, 2005 8:23 pm

I've been lurking and trying to follow understand X-Wings in the hope of solving the V.Hard puzzles but obviously I am not there yet:(

I would be grateful for a pointer to solving the following:

*4* **6 3**
*63 1** **8
58* 3** 7*6
2*6 *15 48*
1*7 *** 6**
8*4 6** 1*9
379 4*2 *61
428 *61 *3*
615 *** **4

As I understand them, I've located an X-wing in Rows 4 and 8 (7 at c4r4 and c9r4 matching with c4r8 and c9r8). Another is at Columns 3 and 8 (1 at c3r1 and c3r3 matching with c8r1 and c8r3).

But I can't get any further forward despite that:(:(

It seems likely that i am missing something obvious and will kick myself when the:idea: dawns!

Or is this an extra hard one which requires different concepts altogether?

Look forward to your input!

George
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Postby Vindaloo » Sat Jun 04, 2005 8:39 pm

This should help:

http://www.sudokusolver.co.uk/step.html

type the following string in as the puzzle (use copy and paste):

_4___63__+_631____8+58_3__7_6+2_6_1548_+1_7___6__+8_46__1_9+3794_2_61+428_61_3_+615_____4
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Postby scrose » Sat Jun 04, 2005 8:55 pm

There is another x-wing in the 2's. Find it and you should be able to reduce r1c3 and r5c8 to one candidate each.
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Postby Animator » Sat Jun 04, 2005 9:04 pm

The X-Wing you are talking about in rows 4 and 8 is an X-wing in the number 7 is correct (btw, please include the number when posting an X-wing).

The one in column 3 and 8 is one in the number 1.

What you are missing (as scrose pointed out) is the X-wing in the number 2. Once you found that you can fill in column 3... (which is easier to see then r5c8, or atleast for the ones who are familiar with the puzzle)
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X-Wing

Postby Guest » Sun Jun 05, 2005 1:38 pm

I have studied this grid and can't see an X-Wing (at least as far as I understand them) in the 2's. Could someone just show me where I am missing it. Thanks
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Postby Animator » Sun Jun 05, 2005 2:13 pm

Here is the grid with the spots marked where the number 2 can go:

* 4 2? | 2? 2? 6 | 3 2? 2?
* 6 3 | 1 2? * | 2? 2? 8
5 8 2? | 3 2? * | 7 2? 6
-----------------------
2 * 6 | * 1 5 | 4 8 *
1 * 7 | 2? 2? * | 6 2? 2?
8 * 4 | 6 2? * | 1 2? 9
-----------------------
3 7 9 | 4 * 2 | * 6 1
4 2 8 | * 6 1 | * 3 *
6 1 5 | * * * | 2? 2? 4


Now take a close look at column 4 and column 9... do you see it? or do you need more help?
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Postby Guest » Sun Jun 05, 2005 3:53 pm

I think I now see what you mean. I was thinking the rows should also not contain any other 2s - i.e only the 4 defining boxes, but of course now I realise that would defeat the object! Thank you - that's solved a mystery for me! Could you also explain a Swordfish in idiot's language? I've looked at Simes' definition but I'm still confused.:)
Guest
 

Postby paulf2127 » Mon Jun 06, 2005 5:27 pm

Ok, I have spent some time on this one; spotted the xwings but am now stuck again.

7 4 1 | x x 6 | 3 9 x
9 6 3 | 1 x x | x 4 8
5 8 2 | 3 x x | 7 1 6
-----------------------
2 x 6 | x 1 5 | 4 8 x
1 x 7 | x x x | 6 5 x
8 5 4 | 6 x x | 1 x 9
-----------------------
3 7 9 | 4 x 2 | x 6 1
4 2 8 | x 6 1 | x 3 x
6 1 5 | x x x | x x 4

I have all my pencil marks shaved right down. Can't see where to go next.
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Postby Animator » Mon Jun 06, 2005 8:00 pm

Next: row 2, after that: row 6, and after that one: row 9...
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And I hoped I understood X-Wings

Postby georgers » Sat Jun 11, 2005 9:38 pm

Just noticed that I never thanked scrose and Animator for the hint that enabled me to solve this one... I understand more now but not enough!
Thanks, guys.....
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