The New Sudoku Players' Forum

[tyrion]

Hello everyone! It's nice to see such a forum. I got addicted to sudoku not long ago and quickly realised the hard ones were the more interesting, although they tend to be the more frustrating too. This one has me completely stuck, and i've used every single logic technique i have, i've even been looking for hidden quads, all that to no avail. This is the puzzle:


1 8 _ 7 2 _ 4 _ _
_ _ _ _ 1 _ _ _ 8
_ 3 _ 4 _ 8 _ 1 _
7 1 _ _ _ _ 2 _ _
5 6 2 1 7 4 9 8 3
_ 9 4 _ _ _ _ 7 _
9 _ 6 _ 8 _ _ _ _
_ 7 _ 9 4 1 _ 6 _
_ _ 1 _ 6 7 _ 9 _

At this point i got stuck, i'd really really appreciate if anybody could help me, at least to the next number. Maybe i'm missing something you won't!

[ronk]

tyrion, welcome to the forum.

As to your puzzle, would you please post your candidate list ... assuming you keep one, of course? The one below is for your puzzle, but you've probably already made some eliminations.

Code: Select all

 *--------------------------------------------------------------------*
 | 1      8      59     | 7      2      3569   | 4      35     569    |
 | 246    245    579    | 356    1      3569   | 3567   235    8      |
 | 26     3      579    | 4      59     8      | 567    1      25679  |
 |----------------------+----------------------+----------------------|
 | 7      1      38     | 3568   359    3569   | 2      45     456    |
 | 5      6      2      | 1      7      4      | 9      8      3      |
 | 38     9      4      | 23568  35     2356   | 156    7      156    |
 |----------------------+----------------------+----------------------|
 | 9      245    6      | 235    8      235    | 1357   2345   12457  |
 | 238    7      358    | 9      4      1      | 358    6      25     |
 | 2348   245    1      | 235    6      7      | 358    9      245    |
 *--------------------------------------------------------------------*


If you're comfortable at a computer, you might also download Angus Johnson's Simple Sudoku. It is designed to give a hint when you ask for one, and generally will give the simplest step available at the time.

[Shazbot]

From Ronk's candidate list above, you can eliminate 3s from box 5 based on locked candidates, a 5 from box 1 based on naked triples, then from box 7 based on locked candidates, and again from box 9 on locked candidates.
Then there's a naked quad 2345 in row 7.

After that an Xwing on 2s (rows 3 and 8, columns 1 and 9) will give you your next placement, and it's plain sailing from there.

If you're not familiar with xwing, you can read up on it here

[Animator]

(Just mentioning for the sake of completeness)

Remeber: if there is a naked group then there must be a hidden group aswell.

If three cells are already known and you found a naked quad then there must be a hidden pair. And guess what? There is one. Hidden pair: 1, 7.

[tyrion]

I thank each of you for your tips, sorry i didn't post my candidate list, i didn't know how to do it (code?).
Anyway, i had indeed found the x wing for the 2s on row 2 and 8, and the naked pair (1,7) on row 7.
And now i feel very ashamed, because that locked candidate 5 on row 8 escaped my attention.. Combined with the x wing, it gives me 4 on r9c9, and the rest is easy.

Hum (feels ashamed)

Well, i thank you very much for your time, I'll try to be more careful! It's nice to know i can get some help if i get stuck too.

[/code]