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Hi

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

Thanks alot!!!

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

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

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

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