Not sure what technique to use here, almost done!

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Not sure what technique to use here, almost done!

Postby iwinsimon » Thu Oct 19, 2017 7:03 pm

Screen Shot 2017-10-19 at 21.55.57.png
Screen Shot 2017-10-19 at 21.55.57.png (93.11 KiB) Viewed 77 times
Hi

This is a medium level puzzle. I don't know which technique to use, any suggestions?

Thanks alot!!!
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Not sure what technique to use here, almost done!

Postby Yogi » Sun Oct 22, 2017 11:19 pm

I had trouble with the picture, but the code is
245763918618.9.73.3978.1.2678613..49.319.867..2967.1838625.739.153.89.679743.685.
This is a BUG+2 situation, which I don't know how to work yet.
Maybe someone can show how that technique would solve this example.
-Yogi
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Re: Not sure what technique to use here, almost done!

Postby Leren » Mon Oct 23, 2017 12:22 am

No BUG but there is a Skyscraper that solves.

Code: Select all
*-----------------------------------*
| 2  4 5 | 7   6   3   | 9   1  8   |
| 6  1 8 | 24  9   245 | 7   3  5-4 |
| 3  9 7 | 8  b45  1   |a45  2  6   |
|--------+-------------+------------|
| 7  8 6 | 1   3   25  | 25  4  9   |
| 45 3 1 | 9   245 8   | 6   7  25  |
| 45 2 9 | 6   7   45  | 1   8  3   |
|--------+-------------+------------|
| 8  6 2 | 5  c14  7   | 3   9 d14  |
| 1  5 3 | 24  8   9   | 2-4 6  7   |
| 9  7 4 | 3   12  6   | 8   5  12  |
*-----------------------------------*

The Skyscraper is in cells a-b-c-d and removes 4 from r2c9 and r8c7. The puzzle then solves in singles.

If you want an introduction to Skyscrapers you can read about them here.

Leon
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Not sure what technique to use here, almost done!

Postby Yogi » Tue Oct 24, 2017 4:29 am

That's interesting. At this point all the unsoved cells are bivalue except r2c6 & r5c5, both of which are (245).
Can you please tell me how you would determine that that this is not a BUG+2 pattern?
- Yogi
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Re: Not sure what technique to use here, almost done!

Postby Leren » Tue Oct 24, 2017 6:01 am

The BUG principle is based on the argument that when all cells are reduced to 2 candidates, each candidate that is not in a solved cell appears exactly twice in its row, column and box.

So let's consider what would happen if we reduced r5c5 to two candidates, considered by dropping out each of its three candidates one at a time.

If it's not 2 or not 4, there would be three 5's in Row 5. If it's not 5 there would be one 5 and three 4's in Column 5.

So the BUG principle cannot be satisfied if r5c5 is reduced to 2 candidates. No BUG.

A link to the definition of BUG is here.

Leren
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