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Re: Sudoku puzzle

  • To: mathgroup at
  • Subject: [mg58428] Re: Sudoku puzzle
  • From: "Jon McLoone" <jonm at>
  • Date: Sat, 2 Jul 2005 04:06:29 -0400 (EDT)
  • References: <d9r4vd$560$><da0fn3$j2a$> <da2n10$94l$>
  • Sender: owner-wri-mathgroup at

Paul Abbott wrote:
> In article <da0fn3$j2a$1 at>,
>  "Jon McLoone" <jonm at> wrote:
> > A short solution, which I placed on Mathsource last week, applies two
> > basic rules before resorting to backtracking. The rules are sufficient
> > to find the 1 at {5,5} in this example.
> >
> >
> Very nice. One thing that would make it more visual is to have an option
> to show progress towards the solution (as was done in the TMJ article).
> Showing the solution a step at a time would be particularly useful if
> you are solving the puzzle by hand, get stuck, and want a hint.

I agree. I added the ShowSteps option as something of an afterthought.
By that point I had already made a logical mistake. The rules I had
implemented consider each row, column and subgrid in isolation. I
hadn't read any literature on Sudoku and this was the way that I
thought I had solved a problem by hand.

As such the row function did not need to know which row it was being
applied to, I just used Map to apply it to all of them. Only the
backtracking code knows where it is working and can report useful
progress data.

At some point I will go back and change this and implement the other
logic referred to in the notebook.

> Since there are many people out there solving Sudoku puzzles, perhaps a
> webMathematica page using your solver would be a nice hook for
> webMathematica and Mathematica?

I dropped a very rough webMathematica version of it on
(No error checking and not very pretty). Perhaps if/when I have
improved the solver, I will clean this up.

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