A tricky one

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A tricky one

Postby luvsudoku » Mon Feb 06, 2006 1:37 am

I've stared at this so long, I must be missing something:
original:
Code: Select all
. . .   1 . .   . . .
. . 2   . . 5   4 . .
5 . .   . 4 .   8 3 .

1 . 5   9 . 2   . . .
4 . .   . . .   . . 8
. . .   8 . 4 ..3 . 5

. 5 3   . 9 .   . . 6
. . 7   5 . .   1 . .
. . .   . . 6   . . .


I got to:
Code: Select all
378  47   48     1    2678 38     59   2567 279
3789 79   2      37   678  5      4    67   1
5    6    1      27   4    9      8    3    27

1    8    5      9    3    2      6    47   47
4    3    9      6    5    7      2    1    8
27   27   6      8    1    4      3    9    5

28   5    3      4    9    1      7    28   6
6    249  7      5    28   38     1    248  2349
289  1    48     237  278  6      59   2458 2349



Any hints for the next step?
luvsudoku
 
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Joined: 29 January 2006

Postby TKiel » Mon Feb 06, 2006 2:32 am

luvsudoku,

Colouring two seperate conjugate chains on candidate 8
Code: Select all
  *-----------*
 |...|1..|...|
 |..2|..5|4.1|
 |561|.49|83.|
 |---+---+---|
 |185|932|6..|
 |439|657|218|
 |..6|814|395|
 |---+---+---|
 |.53|491|7.6|
 |6.7|5..|1..|
 |.1.|..6|...|
 *-----------*
 *-----------------------------------------------------------*
 | 378   47    48A   | 1     2678  38    | 59    2567  279   |
 | 3789B 79    2     | 37    678b  5     | 4     67    1     |
 | 5     6     1     | 27    4     9     | 8     3     27    |
 |-------------------+-------------------+-------------------|
 | 1     8     5     | 9     3     2     | 6     47    47    |
 | 4     3     9     | 6     5     7     | 2     1     8     |
 | 27    27    6     | 8     1     4     | 3     9     5     |
 |-------------------+-------------------+-------------------|
 | 28    5     3     | 4     9     1     | 7     28    6     |
 | 6     249   7     | 5     28    38    | 1     248   2349  |
 | 289   1     48a   | 237   278   6     | 59    2458  234   |
 *-----------------------------------------------------------*

allows the exclusion of 8 in r9c5, which leads to locked candidate 8 in box 8 and exclusion of 8 in r8c8. I don't know if this cracks the puzzle because I haven't followed if further.

Tracy
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Joined: 05 January 2006

Re: A tricky one

Postby QBasicMac » Mon Feb 06, 2006 5:01 am

luvsudoku wrote:Any hints for the next step?


Right. You got to the ridiculously hard stuff. Do coloring, etc., etc., -OR- Do as I do.

Note that r9c7 is either a 5 or a 9. Make a copy of your puzzle. Put 5 in one copy and 9 in the other. Now you have two easy puzzles instead of one difficult. Like differential equations.

One of those two should lead to an impossible case. The other to a solution. If so, you have proved the puzzle has one and only one solution.

Mac
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Postby tarek » Mon Feb 06, 2006 10:40 am

Code: Select all
*--------------------------------------------------------*
| 378   47    48   | 1     2678  38   | 59    2567  279  |
| 3789  79    2    | 37    678   5    | 4     67    1    |
| 5     6     1    | 27    4     9    | 8     3     27   |
|------------------+------------------+------------------|
| 1     8     5    | 9     3     2    | 6     47    47   |
| 4     3     9    | 6     5     7    | 2     1     8    |
| 27    27    6    | 8     1     4    | 3     9     5    |
|------------------+------------------+------------------|
| 28    5     3    | 24    9     1    | 7     248   6    |
| 6     249   7    | 5     28    38   | 1     248   2349 |
| 289   1     48   | 2347  278   6    | 59    2458  2349 |
*--------------------------------------------------------*
r1c5 Must only have 26 as valid Candidates (2569 is a Hidden Quad in Row 1)
r1c8 Must only have 256 as valid Candidates (2569 is a Hidden Quad in Row 1)
r1c9 Must only have 29 as valid Candidates (2569 is a Hidden Quad in Row 1)


Tarek
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Postby TKiel » Mon Feb 06, 2006 2:22 pm

Tarek,

I'm curious why/how you/your solver spotted the hidden quad as opposed to the naked quad (3478) in the same row. Not that I spotted either and I stared at that puzzle for an hour.

Tracy
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Postby tarek » Mon Feb 06, 2006 2:28 pm

Hi Tracy,

The solver goes systematically through combinations, 2569 happens to be smaller (as a whole number) than 3478 & therefore first to be spotted, if it was the other way round then the solver would have spotted the Naked quad first.


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Postby luvsudoku » Mon Feb 06, 2006 5:05 pm

TKiel wrote:Tarek,

..... naked quad (3478) in the same row. Not that I spotted either and I stared at that puzzle for an hour.

Tracy


Thanks you guys - at least I feel better I stared at a while and didn't spot it either. The naked quad solved the puzzle.

I think the 8's conjugate pair thing also solves it....

thanks!
luvsudoku
 
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Joined: 29 January 2006


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