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Help me with this puzzle

 
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gnuvince

Joined: 10 Dec 2006
Posts: 1
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PostPosted: Mon Dec 11, 2006 12:00 am    Post subject: Help me with this puzzle Reply with quote

Hello everyone,

I am writing a sudoku solver in Python that does not use backtracking (that will be another exercise). The results are not bad so far, here are the stats of the program:

Code:

Easy puzzles  : 48 out of 48 (100.00%) puzzles were solved
Medium puzzles: 50 out of 50 (100.00%) puzzles were solved
Hard puzzles  : 32 out of 53 (60.38%) puzzles were solved
Evil puzzles  : 0 out of 54 (0.00%) puzzles were solved


As you can see, my current implementation starts having problems with hard puzzles and can't solve any evil puzzle yet. I would like it if someone could look at the following (incomplete) puzzle and tell me what digit could be logically determined, and work me through the technique. As I found out, just adding one digit to the puzzle can go a long way to solving it.

Code:

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


Thank you for your help,

Edit: the formatting of the puzzle is slightly off because the [ code] tags on this board do not use a fixed-width font. To view it more clearly, copy and paste into Notepad.exe

Vincent.
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m_b_metcalf

Joined: 13 Mar 2006
Posts: 210
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Location: Berlin

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PostPosted: Mon Dec 11, 2006 1:35 am    Post subject: Re: Help me with this puzzle Reply with quote

gnuvince wrote:

As you can see, my current implementation starts having problems with hard puzzles and can't solve any evil puzzle yet. I would like it if someone could look at the following (incomplete) puzzle and tell me what digit could be logically determined, and work me through the technique. As I found out, just adding one digit to the puzzle can go a long way to solving it.


Vincent,
For this type of problem, you can always type your incomplete solution into Sudoku Expainer (use Google to find it), and it will give you the next step with a complete analysis.

HTH

Mike Metcalf
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Pat

Joined: 06 Sep 2006
Posts: 128
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PostPosted: Mon Dec 11, 2006 2:38 pm    Post subject: Reply with quote

gnuvince wrote:

I would like it if someone could look at the following puzzle and tell me what digit could be logically determined, and work me through the technique.

Code:

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




    the 5 for r1
    can only be in box3
    - exclude this digit elsewhere in that box
    ( line-to-box exclusion )

    leaving only one possible digit for r2c8 (not 5)
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Carcul

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

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PostPosted: Wed Dec 13, 2006 6:25 pm    Post subject: Reply with quote

Pat wrote:
leaving only one possible digit for r2c8 (not 5)


After that:

Code:
 *-----------------------------------------------------*
 | 3     1     9   | 6     7     48  | 248   25    458 |
 | 6     7     2   | 38    5     348 | 48    1     9   |
 | 5     8     4   | 2     9     1   | 7     6     3   |
 |-----------------+-----------------+-----------------|
 | 278   4     137 | 9     238   5   | 6     27    18  |
 | 28    6     35  | 7     1     38  | 2348  9     458 |
 | 9     23    157 | 4     238   6   | 238   57    15  |
 |-----------------+-----------------+-----------------|
 | 4     9     8   | 5     6     2   | 1     3     7   |
 | 27    23    37  | 1     4     9   | 5     8     6   |
 | 1     5     6   | 38    38    7   | 9     4     2   |
 *-----------------------------------------------------*

[r9c5]-3-[r9c4]=3=[r2c4]-3-[r2c6]=3|2=[r1c7]-2-[r1c8]=2=[r4c8](-2-
-[r4c5])-2-[r5c7]=2=[r5c1]=8=[r4c1]-8-[(r4c5)]-3-[r9c5], => r9c5<>3 solving the puzzle.

Carcul
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