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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Mon, 30 Mar 2015 01:29:42 -0600
Subject: Re: Sudoku solver
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On Mon, Mar 30, 2015 at 1:13 AM, Christian Gollwitzer <auriocus@gmx.de> wrote:
> Am 30.03.15 um 08:50 schrieb Ian Kelly:
>>
>> On Sun, Mar 29, 2015 at 12:03 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
>>>
>>> Be careful with the benchmark comparisons. Ian's example can be solved
>>> with the identical algorithm in eight different ways (four corners, left
>>> or right). I ran the example with my recent Python solver and got these
>>> times in the eight cases:
>>>
>>>      884   s
>>>        2.5 s
>>>       13   s
>>>      499   s
>>>        5.9 s
>>>      128   s
>>>     1360   s
>>>       36   s
>>
>>
>> That sounds to me like either a transcription error was made to the
>> puzzle at some point, or there's something wrong with your solver. The
>> whole point of that example was that it was a puzzle with the minimum
>> number of clues to specify a unique solution.
>
> I think Marko meant, that if he creates symmetrically equivalent puzzles by
> rotating / mirroring the grid, he gets vastly different execution times, but
> ends up with the same solution.

That makes sense, but it is true for all puzzles that there are eight
possible orientations (since it's impossible for a puzzle solution to
be symmetric), and the wording made it sound like he was describing a
property specific to the puzzle that I posted.