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From: "Frank Millman" <frank@chagford.com>
Subject: Re: constraint based killer sudoku solver performance improvements
Date: Fri, 27 Jan 2012 08:57:10 +0200
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"Blockheads Oi Oi" <breamoreboy@yahoo.co.uk> wrote:

>I have a working program based on [1] that sets up all different 
>constraints for each row, column and box and then sets exact sum 
>constraints for each cage.  It'll run in around 0.2 secs for a simple 
>problem, but a tough one takes 2 hours 45 minutes.  I did some research 
>into improving the performance and found [2] but can't work out how to 
>implement the constraints given.  Can someone please help, assuming that 
>it's even possible.
>
> [1] http://pypi.python.org/pypi/python-constraint/1.1
> [2] http://4c.ucc.ie/~hsimonis/sudoku.pdf

I don't have an answer, but are you aware of this -

http://www.ics.uci.edu/~eppstein/PADS/Sudoku.py

It is a sudoko solver written in pure python.

I don't know what you call a tough problem, but this one solves the hardest 
one I have thrown at it in the blink of an eye. It also outputs a full trace 
of  the reasoning it used to arrive at a solution.

Frank Millman