Difficult sudoku partly solved

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Difficult sudoku partly solved

Postby Obini » Thu Jul 26, 2018 2:53 pm

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


This is a Sudoku partly solved. Please, give me a hint how to proceed (method). I’m stuck!
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Re: Difficult sudoku partly solved

Postby JasonLion-Admin » Thu Jul 26, 2018 3:11 pm

.2.8.361.......3.83.8..927.2.6.1.9..5.16.47824.7..21..8.9...5...4235.8..653...421

Code: Select all
79    2     45    | 8     47    3     | 6     1     459 
179   1679  45    | 12457 2467  1567  | 3     459   8   
3     16    8     | 145   46    9     | 2     7     45   
------------------+-------------------+------------------
2     38    6     | 57    1     578   | 9     345   345 
5     39    1     | 6     39    4     | 7     8     2   
4     389   7     | 59    389   2     | 1     356   356 
------------------+-------------------+------------------
8     17    9     | 1247  2467  167   | 5     36    367 
17    4     2     | 3     5     167   | 8     69    679 
6     5     3     | 79    789   78    | 4     2     1   


A couple of locked candidates lead to a naked pair. After that I would use a unique rectangle and a triple and then it is single to the end.
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Re: Difficult sudoku partly solved

Postby Obini » Thu Jul 26, 2018 5:39 pm

Thank you very much! I've been doing Sudoku for quite some time, but unfortunately I'm not familiar with the terminology. Could you please tell me where I find the locked candidates and the naked pair! That would help me a lot!
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Re: Difficult sudoku partly solved

Postby Obini » Thu Jul 26, 2018 6:50 pm

Thank you, but I need some more help. Unfortunately I'm not very familiar with the terminology. I suppose the naked pair is 1 and 7 in box 7, C1R8 and C2R7. But where are the locked candidates?
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Re: Difficult sudoku partly solved

Postby pjb » Thu Jul 26, 2018 11:02 pm

Hi Obini
This is the grid after naked and hidden singles:
Code: Select all
 79      2       45     | 8      47     3      | 6      1      459   
 179     1679    45     | 12457  2467   1567   | 3      459    8     
 3       16      8      | 145    46     9      | 2      7      45     
------------------------+----------------------+---------------------
 2       38      6      | 57     1      578    | 9      345    345   
 5       39      1      | 6      39     4      | 7      8      2     
 4       389     7      | 59     389    2      | 1      356    356   
------------------------+----------------------+---------------------
 8       17      9      | 1247   2467   167    | 5      36     367   
 17      4       2      | 3      5      167    | 8      69     679   
 6       5       3      | 79     789    78     | 4      2      1     

A solution path after this point is:
7s at r9c456 only ones in row => -7 r7c456, r8c6.
9s at r12c1 only ones in column => -9 r2c2.
Naked pairs of 16 at r78c6 => -1 r2c6, r7c4, -6 r2c6, r7c5
Naked triplets of 579 at r469c4 => -5 r23c4, -7 r2c4
Then it is singles to the end

Phil
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Re: Difficult sudoku partly solved

Postby Obini » Fri Jul 27, 2018 6:14 am

Hi Phil,
thank you very much! This seems to be exactly what I need. I don't have the time now, but I look forward to go through the solution step by step.
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Re: Difficult sudoku partly solved

Postby JasonLion-Admin » Fri Jul 27, 2018 6:46 pm

All the possibilities for 3 in block four are in column 2, so no other candidate for 3 in column 2 can be true. Likwise all of the possibilities for 7 in row 9 are in block 8, so no other candidates for 7 in block 8 can be true. That revelas a naked pair of 16 in R78C6 whil eliminates all other candidates for 1 and 6 in column 6.
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