The New Sudoku Players' Forum

[domz]

Hey there,

I got stuck on this puzzle and am running out of ideas, maybe someone can have a look and give me some hints?

This is the original grid:

Code: Select all

. . 7 | . 5 . | 6 . 4
4 . . | . . . | . . 9
. 8 . | 4 . . | 1 3 .
------+-------+------
. 6 . | . . . | 9 2 .
. . . | 1 . 3 | . . 8
. . . | 9 . 4 | . . .
------+-------+------
6 . . | 5 . . | 8 . 2
. . . | 7 . . | . . 1
8 5 . | . 4 . | 3 . .


and i got it this far now:

Code: Select all

. . 7 | . 5 . | 6 8 4
4 . . | . . . | 2 . 9
. 8 . | 4 9 . | 1 3 .
------+-------+------
1 6 4 | 8 7 5 | 9 2 3
7 . . | 1 . 3 | 4 . 8
. . 8 | 9 . 4 | 7 1 .
------+-------+------
6 7 . | 5 . . | 8 4 2
. 4 . | 7 . . | 5 . 1
8 5 . | . 4 . | 3 . .


and with pencil marks:

Code: Select all

239  1239  7   | 23  5   23   | 6  8   4
4    13    356 | 36  18  1678 | 2  57  9
25   8     26  | 4   9   267  | 1  3   57
---------------+--------------+----------
1    6     4   | 8   7   5    | 9  2   3
7    29    259 | 1   26  3    | 4  56  8
235  23    8   | 9   26  4    | 7  1   56
---------------+--------------+----------
6    7     139 | 5   13  19   | 8  4   2
239  4     239 | 7   38  2689 | 5  69  1
8    5     129 | 26  4   1269 | 3  679 67


But now i can't find any more (hidden) subsets, or skyscrapers or other patterns i'm familiar with.
I'm not too good with fish, so there's maybe a fish hiding here somewhere which i missed?

Hope i made no mistakes on the way and would be really thankful if someone could point me to the next steps or techniques i could try.

Much thanks,
.dom

[eleven]

Hi Dom,

there is a typo in your grid, r1c6 should be 12.

Also after using the x-wing 5 (-5r3c3) i can't find a solution without using chains.
But it is a nice example for our one-step game (in the Puzzles thread).

Code: Select all

 *----------------------------------------------------------*
 |  239   1239   7     |  23   5    12     |  6  8     4    |
 |  4     1-3   c356   | c36   18   1678   |  2  57    9    |
 |  25    8      256   |  4    9    267    |  1  3     57   |
 |---------------------+-------------------+----------------|
 |  1     6      4     |  8    7    5      |  9  2     3    |
 |  7    b29    b259   |  1    26   3      |  4  56    8    |
 |  235  a23     8     |  9    26   4      |  7  1     56   |
 |---------------------+-------------------+----------------|
 |  6     7      139   |  5    13   19     |  8  4     2    |
 |  239   4      239   |  7    38   2689   |  5  69    1    |
 |  8     5      129   |  26   4    1269   |  3  679   67   |
 *----------------------------------------------------------*

(3=2)r6c2 - (2=95)r5c23 - (5=36)r2c34 => -3r2c2, stte
In words:
If r6c2 is not 3, it must be 2, and r5c2=9 and r5c3=5. Then r2c3 is not 5 and together with r2c4 it gives a pair 36.
So either you have r6c2=3 or r2c34=36, and you can eliminate 3 from r2c2 (leaving only singles to the end)

[Leren]

After the X wing mentioned by eleven the grid looks like this:

Code: Select all

*-------------------------------------------*
| 239 1239 7   | 23 5   12   | 6  8     4   |
| 4   13   356 | 36 18 d1678 | 2 e57    9   |
| 25  8    26  | 4  9   267  | 1  3     5-7 |
|--------------+-------------+--------------|
| 1   6    4   | 8  7   5    | 9  2     3   |
| 7   29   259 | 1  26  3    | 4  56    8   |
| 235 23   8   | 9  26  4    | 7  1     56  |
|--------------+-------------+--------------|
| 6   7    139 | 5  13  19   | 8  4     2   |
| 239 4    239 | 7  38 c2689 | 5 b69    1   |
| 8   5    129 | 26 4   1269 | 3  69-7 a67  |
*-------------------------------------------*

Then a chain in cells a-b-c-d-e : (7=6) r9c9 - r8c8 = (6-8) r8c6 = (8-7) r2c6 = (7) r2c8 => - 7 r3c9, r8c7, stte

I wont go through the wordy description like eleven did, but it shows that at least one of cell a or cell e must be 7, so cells seeing both of these can't be 7, which leads to the two eliminations.

As per eleven, the puzzle then solves with a cascade of singles.

Leren

[domz]

Hi,

Much thanks for the quick replies and pointing out those chains @eleven and @Leren!

I would never ever found those myself.. are there some tricks and tactics to find chains or is it just trial and error?

Thanks again for your help,
.dom

[eleven]

.. are there some tricks and tactics to find chains or is it just trial and error?

The simple trick is to ask programs. Another one to make markups, which show you possibly useful links.
And it needs trial & error (by users or programs), though there is made some effort to hide that in the presentation of a move.
The best trick is practise (including looking at other's solutions).

[domz]

Ok, thanks for the feedback!