The New Sudoku Players' Forum

[Gero]

Hi everyone,

I'm new to the forum. Until now I was able to solve every hard Sudoku that I tried, but now I am stuck on this one. I never learned any solving technique by hard, for this one I looked into the advanced techniques, but they all seemed like kind of what I am already applying. Of course I could be bruteforcing it, but I hope to find a more elegant method.
It would be great if someone could tell me what a next step in this state is.

Thanks in advance
Gero

[jco]

Hello Gero,

Code: Select all

.---------------------------------------------.
| 8   14-7 39  | 2  d(17)  5   | 6   19  347  |
| 5 b(1)47 36  | 9    68 c(1)37| 37  2   3478 |
| 2 a(17)  369 | 68   4    13-7| 5   19  378  |
|--------------+---------------+--------------|
| 37  9    1   | 4    2    8   | 37  5   6    |
| 37  6    8   | 37   5    9   | 1   4   2    |
| 4   5    2   | 367  167  17  | 9   8   37   |
|--------------+---------------+--------------|
| 9   8    7   | 5    3    4   | 2   6   1    |
| 1   2    5   | 78   78   6   | 4   3   9    |
| 6   3    4   | 1    9    2   | 8   7   5    |
'---------------------------------------------'

You have a strong link of 1s in row 2. If r3c2 is not 7, then it can only be 1, so r2c2 cannot be 1, so that r2c6 has to be 1. If r2c6 is 1, r1c5 has to be 7. So, r1c2 cannot be seven, if r3c2 is not 7. Of course, the same happens if r3c2 = 7, so 7 is false in r1c2. As a by-product r3c6 also cannot be 7.
This is the so-called W-wing. After this you need to find a skyscraper on 7.
Regards,
jco

Edit: image gone, so included grid for this nice puzzle.

[Gero]

Hi jco,
thanks a lot for the well explained answer. With this tip I was able to solve the puzzle.
Best regards,
Gero

[jco]

Hello Gero,

Thanks for the feedback. That was a good puzzle. From your message and very accurate markings, I knew that you would finish it quickly.

Code: Select all

.-------------------------------------------------.
| 8   147  39  | 2    17    5    |  6    19  347  |
| 5   147  36  | 9    68   b13(7)| c3(7) 2   3478 |
| 2   17   369 | 68   4     137  |  5    19  378  |
|--------------+-----------------+----------------|
| 37  9    1   | 4    2     8    | d3(7) 5   6    |
| 37  6    8   | 37   5     9    |  1    4   2    |
| 4   5    2   | 367  167  a1(7) |  9    8   3-7  |
|--------------+-----------------+----------------|
| 9   8    7   | 5    3     4    |  2    6   1    |
| 1   2    5   | 78   78    6    |  4    3   9    |
| 6   3    4   | 1    9     2    |  8    7   5    |
'-------------------------------------------------'

Skyscraper => -7 r6c9

Best regards,
JCO

Edit: added grid with SS move.