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I give up! - any suggestions please?

 
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Guest
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PostPosted: Sat Oct 15, 2005 10:24 am    Post subject: I give up! - any suggestions please? Reply with quote
Can't see where to move now ......

Code:

1    568   4    2    56  7   3568 36  9   
256  9     2568 356  4   13  1568 7   156 
3567 567   3567 8    156 9   156  2   4   
46   2     168  346  9   138 7    5   1368   
4567 15678 9    3456 156 138 2    136 1368   
56   3     18   56   7   2   9    4   18   
2367 67    2367 1    8   4   356  9   2356   
9    4     126  7    3   5   16   8   126 
8    15    135  9    2   6   4    13  7   
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
PostPosted: Sat Oct 15, 2005 11:57 am    Post subject: Re: I give up! - any suggestions please? Reply with quote
Guest wrote:
Can't see where to move now ......

Code:

1    568   4    2    56  7   3568 36  9   
256  9     2568 356  4   13  1568 7   156 
3567 567   3567 8    156 9   156  2   4   
46   2     168  346  9   138 7    5   1368   
4567 15678 9    3456 156 138 2    136 1368   
56   3     18   56   7   2   9    4   18   
2367 67    2367 1    8   4   356  9   2356   
9    4     126  7    3   5   16   8   126 
8    15    135  9    2   6   4    13  7   

You have an "X-Wing" formation in the 1's. There are only two places in column 2 where a "1" can appear (r5c2 & r9c2). Similarly there are only two places in column 8 where a "1" can appear (r5c8 & r9c8). Since there MUST be a "1" at either r5c2 & r9c8, or at r5c9 & r9c2, you can eliminate the possibility of a "1" at other places in rows 5 and 9. Specifically, "1" cannot appear at r5c5, r5c6, r5c9, or r9c3.

Now you can place a "1" at r3c5 and at r4c6, and make some more progress. dcb Smile
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SR



Joined: 12 Oct 2005
Posts: 21
Location: Cornwall
PostPosted: Sat Oct 15, 2005 12:02 pm    Post subject: Reply with quote
Ah! Now I understand x-wing.
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Guest
Guest
PostPosted: Sat Oct 15, 2005 7:14 pm    Post subject: THANK YOU DAVID! Reply with quote
That is the clearest explanation of an X Wing I have seen. For some reason, with an X Wing, I thought I had to look for pairs. Thanks again. Very Happy
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
PostPosted: Sat Oct 15, 2005 7:44 pm    Post subject: You're welcome Reply with quote
I'm glad I could help.

If you're interested in understanding another "advanced technique" you might want to look at "A very tough minimal Sudoku," "XY-Wing Example #1," "XY-Wing Example #2," and "XY-Wing Example #3" in this "Other Puzzles" forum. dcb
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Guest
Guest
PostPosted: Sat Oct 15, 2005 9:59 pm    Post subject: To David Reply with quote
Yes - I am aware of those you mention and intend to study them when I've got time!!! You are a very helpful contributor and offer clear explantions which is appreciated.
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