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Sudoku from Stern

 
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Iavor

Joined: 14 Jun 2006
Posts: 1
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Location: Berlin

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PostPosted: Wed Jun 14, 2006 7:57 am    Post subject: Sudoku from Stern Reply with quote

The german magazin "Stern" publish sudokus. In the issue from 8.6.2006 (Nr 24, page 189) there was a sudoku "KAMIKAZE", where Simple Sudoku couldn't help:
Code:
 *-----------*
 |6..|...|..4|
 |.3.|...|.9.|
 |..1|479|3..|
 |---+---+---|
 |..3|6.5|8..|
 |946|...|513|
 |..2|1.3|9..|
 |---+---+---|
 |..7|824|6..|
 |.2.|...|.8.|
 |8..|...|..1|
 *-----------*

After several quite simple steps I come to (confirmed with the solving mode of Simple Sudoku):
Code:
 *-----------*
 |6..|...|..4|
 |.3.|...|.9.|
 |251|479|368|
 |---+---+---|
 |..3|695|842|
 |946|782|513|
 |582|143|976|
 |---+---+---|
 |..7|824|6..|
 |.2.|...|.8.|
 |86.|..7|..1|
 *-----------*

or
Code:
 *-A----B----C------D----E----F------G----H----I----*
 | 6    79   89   | 235  13   18   | 127  25   4    |
 | 47   3    48   | 25   156  168  | 127  9    57   |
 | 2    5    1    | 4    7    9    | 3    6    8    |
 |----------------+----------------+----------------|
 | 17   17   3    | 6    9    5    | 8    4    2    |
 | 9    4    6    | 7    8    2    | 5    1    3    |
 | 5    8    2    | 1    4    3    | 9    7    6    |
 |----------------+----------------+----------------|
 | 13   19   7    | 8    2    4    | 6    35   59   |
 | 34   2    459  | 359  16   16   | 47   8    79   |
 | 8    6    459  | 359  35   7    | 24   23   1    |
 *--------------------------------------------------*

Further no hint is available. Questions: Rolling Eyes

1. Is the following way legitimate or just guess (invalid)?

if A4 is 1, than
A7=3, A8=4, H7=5, I7=9, I8=7, G8=4
but A8 was already 4, therefore A4 cannot be a 1. Twisted Evil

The final solution: Idea
Code:

 *-----------*
 |679|318|254|
 |438|256|197|
 |251|479|368|
 |---+---+---|
 |713|695|842|
 |946|782|513|
 |582|143|976|
 |---+---+---|
 |197|824|635|
 |324|561|789|
 |865|937|421|
 *-----------*

2. Is there another logical solution here? Question
Cheers
iavor
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rkral

Joined: 21 Oct 2005
Posts: 233
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PostPosted: Wed Jun 14, 2006 12:50 pm    Post subject: Re: Sudoku from Stern Reply with quote

Iavor wrote:
1. Is the following way legitimate or just guess (invalid)?

if A4 is 1, than
A7=3, A8=4, H7=5, I7=9, I8=7, G8=4
but A8 was already 4, therefore A4 cannot be a 1.

Perfectly logical deduction. You don't need to include A4, however.

A7=3, H7=5, I7=9, I8=7, G8=4, A8=3, A7<>3, implies A7<>3

Iavor wrote:
2. Is there another logical solution here? Question

It can be shown that D8 cannot be a 3 by using cells A8 and the almost-locked-set in C9, D9, and E9.
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Carcul

Joined: 29 Dec 2005
Posts: 50
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Location: Coimbra, Portugal

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PostPosted: Thu Jun 15, 2006 4:24 pm    Post subject: Another Solution Reply with quote

C9=9 or G1=2. But G1=2 => G9=4. So C9 cannot be 4 and the puzzle is solved.

Carcul
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maarten

Joined: 16 Jun 2006
Posts: 7
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Location: The Netherlands

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PostPosted: Mon Jul 10, 2006 1:25 pm    Post subject: Reply with quote

Hehe, my solver finds a XY Chain of 15 steps, and of course a different number and cell. Cool Very Happy

Found a Naked Single - added a 8 in cell (5,5)
Found a Naked Single - added a 4 in cell (6,5)
Found a Naked Single - added a 9 in cell (4,5)
Found a Hidden Single in row 4 - added a 4 in cell (4,8)
Found a Hidden Single in row 4 - added a 2 in cell (4,9)
Found a Hidden Single in column 2 - added a 6 in cell (9,2)
Found a Naked Single - added a 7 in cell (9,6)
Found a Naked Single - added a 2 in cell (5,6)
Found a Naked Single - added a 7 in cell (5,4)
Found a Hidden Single in row 6 - added a 8 in cell (6,2)
Found a Naked Single - added a 5 in cell (3,2)
Found a Naked Single - added a 2 in cell (3,1)
Found a Naked Single - added a 6 in cell (3,8)
Found a Naked Single - added a 8 in cell (3,9)
Found a Naked Single - added a 7 in cell (6,8)
Found a Naked Single - added a 5 in cell (6,1)
Found a Naked Single - added a 6 in cell (6,9)
Found a Locked Candidate 1 in row 7 - removing candidate from cells (8,1)
Found a Locked Candidate 5 in row 7 - removing candidate from cells (8,9),(9,8)
Found a Hidden Double 1/6 in row 8 - removing other candidate from cells (8,5),(8,6)
Found an XY-Chain-15 from cell (1,2) to cell (8,7), resulting in removal of candidate 7 in cells (1,7)
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