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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Mon, 30 Mar 2015 00:50:01 -0600
Subject: Re: Sudoku solver
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On Sun, Mar 29, 2015 at 12:03 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
> BartC <bc@freeuk.com>:
>
>> As Chris mentioned, when I say 'faster than C', I mean X running my
>> algorithm was faster then C running Marko's algoritim (on Ian's data).
>> This was just an illustration of algorithm being more important than
>> language.
>
> 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 tried entering that puzzle into the solver at
http://www.sudoku-solutions.com/. It confirms that there is a unique
solution, and the solution it gives matches the one given in the
article as well as the solution that I got from Norvig's solver.

Also, Frank Millman successfully ran the Eppstein solver on it
upthread, which purportedly should complain if the puzzle does not
have a unique solution.