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April 19th

 
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msgraciey



Joined: 02 May 2007
Posts: 6
PostPosted: Wed May 02, 2007 8:10 pm    Post subject: April 19th Reply with quote
> Sorry to write for help...I am stuck and the hints give a "9" at > r1c3 and 43c4. I put the puzzle in on scanraid and at the point I'm > at, it shows a simple chain or coloring involving the 29s at > r1c3,r3c2,r4c3,r7c1,r8c2 and r8c8. It says this eliminates the 2 at > r1c8. I read the explanations but I just don't get it. I also tried > the process of elimination-if this, then that, but that didn't help > either. Thanks so much!
>
> [code]
> +-----------+-------------+-------------+
> | 15 3 29 | 1789 18 6 | 4 25 27 |
> | 7 8 6 | 5 4 2 | 39 1 39 |
> | 15 29 4 | 179 3 79 | 8 256 267 |
> +-----------+-------------+-------------+
> | 8 5 29 | 3 12 4 | 6 7 129 |
> | 269 4 7 | 19 126 5 | 129 3 8 |
> | 269 1 3 | 789 268 79 | 29 4 5 |
> +-----------+-------------+-------------+
> | 29 67 1 | 4 5 8 | 237 269 236 |
> | 3 29 8 | 6 7 1 | 5 29 4 |
> | 4 67 5 | 2 9 3 | 17 8 16 |
> +-----------+-------------+-------------+
> Grace Yrizarry
> .
> Grovetown, GA
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Thu May 03, 2007 12:05 am    Post subject: Re: April 19th Reply with quote
msgraciey wrote:
> Sorry to write for help...I am stuck and the hints give a "9" at > r1c3 and 43c4. I put the puzzle in on scanraid and at the point I'm > at, it shows a simple chain or coloring involving the 29s at > r1c3,r3c2,r4c3,r7c1,r8c2 and r8c8. It says this eliminates the 2 at > r1c8. I read the explanations but I just don't get it. I also tried > the process of elimination-if this, then that, but that didn't help > either. Thanks so much!


Here's what I'm seeing, a technique called "Remote Pairs."

Code:
> +-----------+-------------+-------------+
> | 15  3   29- | 1789 18  6  | 4   25   27 |
> | 7   8   6   | 5    4   2  | 39  1    39 |
> | 15  29+ 4   | 179  3   79 | 8   256  267|
> +-----------+-------------+-------------+
> | 8   5  29   | 3    12  4  | 6   7    129|
> | 269 4   7   | 19   126 5  | 129 3    8  |
> | 269 1   3   | 789  268 79 | 29  4    5  |
> +-----------+-------------+-------------+
> | 29  67  1   | 4    5   8  | 237 269  236|
> | 3   29- 8   | 6    7   1  | 5   29+   4 |
> | 4   67  5   | 2    9   3  | 17  8    16 |
> +-----------+-------------+-------------+


Note the four cells with a 29 pair that I've marked + or -. The + and - means that as you go through the chain, if one cell is one thing, then the next cell must be the other. For example, if the first cell in the chain is a 2, the next must be 9, etc.

So r1c3 and r8c8 must be 29 or 92, it doesn't matter which is which. Any cell which sees both ends of the chain cannot be a 2 or 9. In this case, that cell is r1c8 which can't be 2 or 9, thus it's got to be 5. These chains have to be an even number of cells, or else the two ends of the chain will have the same polarity, so to speak.
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msgraciey



Joined: 02 May 2007
Posts: 6
PostPosted: Thu May 03, 2007 2:23 am    Post subject: Reply with quote
Ah! I think I understand your explanation! When I went back and thought it through it made sense. Will proceed on from there, and thanks again!
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Mogulmeister



Joined: 03 May 2007
Posts: 1151
PostPosted: Thu May 03, 2007 11:54 am    Post subject: Reply with quote
For simplicity also note that the colouring path shown by Marty will work just on the 2's - it is not entirely necessary to involve the 9's although that would have been ultra powerful if r1c8 had contained a 9 as well.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Fri May 04, 2007 12:56 am    Post subject: Reply with quote
> For simplicity also note that the colouring path shown by Marty will
> work just on the 2's - it is not entirely necessary to involve the 9's
> although that would have been ultra powerful if r1c8 had contained
> a 9 as well.

Yes, but pairs are much easier to grasp. Remote pairs are actually coincident coloring on two numbers. A remote pair which leads to elimination of a single candidate is actually coloring with easily identified strong links.

So, for example, Sudoku Susser uses Remote Pairs as a fairly easy technique. It does not do coloring.

Keith
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dulaby



Joined: 02 May 2007
Posts: 13
PostPosted: Fri May 04, 2007 6:50 pm    Post subject: Reply with quote
I solved that one using an xyz-wing: R3C4(179),R3C6(79) and r5c4(19) so that <9> is out of R1C3 and R1C3 has to be<9>.
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dulaby



Joined: 02 May 2007
Posts: 13
PostPosted: Fri May 04, 2007 6:58 pm    Post subject: Reply with quote
Sorry ,<9> is out of R1C4 and R1C3 has to be 9.
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Mogulmeister



Joined: 03 May 2007
Posts: 1151
PostPosted: Mon May 07, 2007 2:59 pm    Post subject: Reply with quote
Quote:
Sorry to write for help...


Don't be sorry Grace - that's what this place is for ! Smile
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