Completely stuck and in need of help please.

Advanced methods and approaches for solving Sudoku puzzles

Completely stuck and in need of help please.

Postby zebedee » Thu Jun 09, 2005 6:21 pm

Despite spending a good few hours on the very hard puzzle shown below, I'm stumped as to how proceed. Can anyone more skilled in the art of completing very hard Sudoku puzzles kindly point me in the right direction with a small clue? I suspect there is an X-wing somewhere but I can't see it for looking.

Thanks in anticipation.

Zeb

PS I manage to complete 1 in 3 very hard puzzles but this one is beyond me!

*** *** 725
**7 *** *4*
*5* 3*7 **1

581 94* *37
*** *8* *5*
*4* *53 8**

375 6*8 *9*
*2* *** 5**
61* *** ***
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Postby Animator » Thu Jun 09, 2005 7:01 pm

First look at box 5, and ask yourself this question: where can the number 7 go?

Then take a really good look at row 8 (and remember what you said about box 5). If you look carefully you will see a group of 3 numbers that occupies the exact same three cells... this allows you to remove all other candidates from these cells.

And that finally allows you to fill in a number in box 9.
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Postby zebedee » Thu Jun 09, 2005 9:29 pm

Thanks for your E-mail animator.

I note that the number 7 can only go in c4,r5 or c4,r6 of Box 5 but I can't see any combination of three numbers in r8 which might allow me to remove other possible numbers.

My r8 pencilmarks are as follows:

c1,r8 - 4/8/9
c2,r8 - Contains number 2
c3,r8 - 4/8/9

c4,r8 - 1/4
c5,r8 - 1/3/7/9
c6,r8 - 1/4/9

c7,r8 - Contains number 5
c8,r8 - 1/6/7/8
c9,r8 - 3/6/8

Any additional help that you can provide would be appreciated please.

Zeb
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Postby Roz » Fri Jun 10, 2005 1:41 am

edit: Sorry, replied then realised your pm's are not exactly the same as mine so will let Animator or someone else more advance than myself reply.
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Postby Arnie » Fri Jun 10, 2005 6:19 am

Zeb..

r8c5 and r9c5 must have a pair ...so you can eliminate 2 numbers from those you've got in c5,r8.

secondly, look carefully at which cells in row 8 the numbers 3,6 and one other number can go in....
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Postby Animator » Fri Jun 10, 2005 10:03 am

The group of numbers you should be looking for on row 8 are:
* first group: 3, 6, 7
* second group: 1, 4, 8, 9

Arnie is right that you can remove some candidates from r8c5 but if you see the groups on row 8 then you will remove exaclty the same candidates :)
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Postby zebedee » Sat Jun 11, 2005 2:53 pm

Arnie/Animator,

Many thanks for your kind advice. I've now solved the puzzle. I was looking for an X-wing that wasn't there and missed other, perhaps easier to spot, clues.

Zeb

:)
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