200e200w's Nightmare #1

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200e200w's Nightmare #1

Postby 200e200w » Sat Jan 27, 2018 9:38 pm

Code: Select all
. . 2|. . 6|. 3 .
. 8 .|. 4 .|. . .
9 . .|. . .|. . .
-----+-----+-----
. . .|. . 7|5 . .
. 3 .|. 1 .|9 8 .
2 . .|5 . .|. 7 3
-----+-----+-----
. . .|4 8 .|. 9 .
5 . .|. 7 1|8 . 2
. . .|. . 5|. 4 .

Enjoy solving!

200e200w
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Re: 200e200w's Nightmare #1

Postby pjb » Sat Jan 27, 2018 10:36 pm

Found no single solution
I found a continuous chain:
r1c4 = (8-9)r1c9 = r2c9 - r2c6 = (9-8)r6c6 = r3c6 - loop => -9 r2c4, -8 r3c4, -47 r1c9, -4 r6c6
then a Sashimi swordfish of 4s:
r3c239, r6c37, r8c23 => -4 r4c9; lclste

Phil
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Re: 200e200w's Nightmare #1

Postby 200e200w » Sun Jan 28, 2018 8:48 am

Hi, Phil!
Found no single solution

I agree: this sudoku has no single-step solution (tested).
...a Sashimi swordfish of 4s:
r3c239, r6c37, r8c23 => -4 r4c9; lclste

This solution is correct, but first, you can also eliminate 4 from r1c7 using this, and second, I would instead use a Skyscraper:
Code: Select all
.---------------------.---------------------.---------------------.
|d14     1457   2     | 1789   59     6     | 7-4    3      89    |
| 136    8      1367  | 137    4      239   | 26     5      79    |
| 9      567-4  367-4 | 37     235    238   | 26     1     a478   |
:---------------------+---------------------+---------------------:
|c1468   1469   14689 | 3689   369    7     | 5      2     b14    |
| 7      3      5     | 2      1      4     | 9      8      6     |
| 2      1469   14689 | 5      69     89    | 14     7      3     |
:---------------------+---------------------+---------------------:
| 136    1267   1367  | 4      8      23    | 137    9      5     |
| 5      49     349   | 39     7      1     | 8      6      2     |
| 138    1279   13789 | 369    2369   5     | 137    4      17    |
'---------------------'---------------------'---------------------'
(4)r3c9 = r4c9 - r4c1 = r1c1 => -4 r1c7,r3c23; lclste


200e200w
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Re: 200e200w's Nightmare #1

Postby Leren » Sun Jan 28, 2018 10:32 am

200e200w said : I agree: this sudoku has no single-step solution (tested).

Actually there is one : Eliminate 4 in r8c2 for an stte finish.

Easier said than done !

Leren
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Re: 200e200w's Nightmare #1

Postby 200e200w » Sun Jan 28, 2018 10:59 am

Actually there is one : Eliminate 4 in r8c2 for an stte finish.

Yes, but there is no logical way to prove this elimination in one step. Tested with SudoCue and Sudoku Explainer.

200e200w
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