Irritating logic for this puzzle

Advanced methods and approaches for solving Sudoku puzzles

Irritating logic for this puzzle

Postby axis » Thu Jun 09, 2005 11:36 pm

I edited this post, hopefully to make it more clear on the logic reading, sorry the graphic isn't better.

Hey, I was trying to do the puzzled on sudoku.com. If you click on syndication its the puzzle in the newspaper example. Anyways, I got to the following point:

314 627 **8
925 148 637
*** **5 124
43* 8*6 **2
*** 572 4*3
*52 **4 *86
596 783 241
*4* 269 375
273 451 869


Anyways, the only way I know to go from here stems from this logic:

In r5c8 the only thing able to go there is a 9 or 1. If I put a 9 there then a 1 has to in r4c8 and a 7 in r6c7. Thus a 1 must go in r6c1 and a 9 in r4c5. And a 3 in r3c5. Thus that means a 1 must go in r6c5 when I already have a 1 in r6c1. Thus a contradiction meaning I should put a 1 in r5c8.


Now it seems to me that that is a huge undertaking and there should be some simpler form of logic. Any help here? Thanks.[/quote]
axis
 
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Postby paulf2127 » Fri Jun 10, 2005 12:38 am

You are right that the 1 and 9 have to go in r4c8, r5c8. The logic now though is you can place the 5 in r1c8 as this is the only place it can go.

Next complete box 3 and then complete column 7. This will allow you to place the 7 in box 4.

This 7 allows you to work out which way round the numbers in box 1 go and you can fill that in.

Now drop down to box 7 and mop that up. Then columns 2 and 3 have only one number each left. Fill away.

This allows you to look across and complete box 6 getting the 1 and 9 in the right order. Downhill from there.
paulf2127
 
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Postby paulf2127 » Fri Jun 10, 2005 12:53 am

However, this is using tril and error which is a bit of a no-no.

Having mapped the puzzle, I don't believe this can be solved without making a guess. It may not be a pappacom one.

Animator will tell you one way or the other. He's the man.
paulf2127
 
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Postby axis » Fri Jun 10, 2005 12:55 am

However, is the best way to figure out the 9 and 1 spot, by going through all that? Or is there another number or spot to start with that makes it much easier?
axis
 
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Postby sud_grrl » Fri Jun 10, 2005 1:05 am

Forget about places where you have to guess ...
in R3C1, you have missed out the 8 that was entered on the puzzle - this allows you to place other 8s in that series of 3 columns - in C2, it must go in R5 as this is the only option, then you can also enter the one in C3, which now must go in R8 ...

This leaves you with on ly 6 & 7 to go in that square, ang you can use C2 and C3 to work those out then go from there:)
sud_grrl
 
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