how to solve ..

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how to solve ..

Postby Drjay » Tue Aug 18, 2015 7:30 pm

Hey guys,

how to solve this?

Image

Mention the technique to solve this please :)

Thanks in advance!
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Re: how to solve ..

Postby JasonLion » Tue Aug 18, 2015 8:21 pm

I would use a Sashimi X-Wing, though there are doubtless other approaches that would also work.

..4....2.8.1..2.465324...89..8.49.32329..86.44..2..9.8.8.5..49..4............4.61
Last edited by JasonLion on Tue Aug 18, 2015 9:58 pm, edited 1 time in total.
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Re: how to solve ..

Postby Drjay » Tue Aug 18, 2015 8:39 pm

What other techniques could I use? Thanks anyways.
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Re: how to solve ..

Postby Leren » Tue Aug 18, 2015 9:04 pm

The simplest technique to use is a Skyscraper, which I'll illustrate here.

Code: Select all
*--------------------------------------------------------------------------------*
| 679     679     4        | 13789   135789  1357     | 1357    2       57       |
| 8       79      1        | 379    b3579    2        |a357     4       6        |
| 5       3       2        | 4       167     167      | 17      8       9        |
|--------------------------+--------------------------+--------------------------|
| 67      1567    8        | 167     4       9        |*7-5     3       2        |
| 3       2       9        | 17     c157     8        | 6      d157     4        |
| 4       1567    567      | 2       13567   13567    | 9       157     8        |
|--------------------------+--------------------------+--------------------------|
| 1267    8       367      | 5       12367   1367     | 4       9       37       |
| 12679   4       367      | 136789  1236789 1367     | 28      57      357      |
| 279     579     357      | 3789    23789   4        | 28      6       1        |
*--------------------------------------------------------------------------------*

Look at the cells I've marked abcd. Notice that there are only two 5's in Rows 2 and 5. If cell a was not 5 cell b would have to be 5 (only 2 5's in Row 3), so cell c would not be 5, so cell d would be 5 (2 5's in Row 5).

Reversing this argument, and assuming cell d was not 5 and following the path bcda you would have to conclude that cell a would be 5.

The result of all this is that at least one of cells a and d must be 5. They could both be 5 but they can't both be not 5.

Now look at cell r4c7, which I've marked with a *. Since it can see both cells a and d it can't be 5. You can remove the 5 from that cell, so it's 7 and the puzzle solves easily from there.

Here's a link to a good teaching site that discusses Skyscrapers and a lot of other solving techniques.

http://hodoku.sourceforge.net/en/techniques.php

PS: Jason's Sashimi Finned XWing and the Skyscraper use the same cells, but the XWing reasoning is a bit more involved. Sashimi Finned XWings are also discussed on the Hodoku site.

PPS: I can't see how you removed the 9 from r8c5. Maybe it's a limitation of your graphic, which looks like it can only accommodate 6 candidates in a cell.

Leren
Last edited by Leren on Tue Aug 18, 2015 9:26 pm, edited 3 times in total.
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Re: how to solve ..

Postby Leren » Tue Aug 18, 2015 9:05 pm

Hi Jason, there appears to be a typo in your line format version of this puzzle. I can see a 1 missing from the end.

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Re: how to solve ..

Postby JasonLion » Tue Aug 18, 2015 9:59 pm

Leren wrote:Hi Jason, there appears to be a typo in your line format version of this puzzle. I can see a 1 missing from the end.


Thanks for catching that. Fixed now.
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