Message: 14
Date: Sun, 31 Jul 2005 15:13:08 +0100
From: Alex Tweedly <[EMAIL PROTECTED]>
Subject: Re: ANN: Sudoku Assistant
To: How to use Revolution <[email protected]>
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Jim Hurley wrote:
Alex,
Thanks for the puzzle. Lots of fun. Dell Crosswords has a full page of
these every month, though none as tough a your last. They generally
are deterministic all the way to the end. Your number four requires
assuming a solution at one point near the end and discovering a
contradiction if the guess was wrong--proof by contradiction.
No, it doesn't require that. There's a perfectly deterministic technique
that can solve puzzle #4 - I'll append a brief description of it to the
end of this message - but beware it uses puzzle #4 to demonstrate it, so
don't read all the way to the end unless you want to read that ...
I used the wrong word when I said "deterministic." What I should
have said was that puzzle 4 requires a *two* stage decision making
process. In the simpler puzzles at each step there is always one
square in which there is obviously only one possibility--a one stage
decision making process.
In the fourth puzzle I reach a point where there is no square which
would allow only one character. But if I put one character in this
square then I will run into a contraction at a later stage. But if I
put another character into the square, I will be able to obtain a
unique solution. As you say, this is still a deterministic solution,
but a two stage deterministic process. Sorry for the poor description
of what I was trying to say.
> (I must confess that the labels make it more difficult for me--harder
to see what is filled in and what isn't.)
Sorry Jim I'm not sure I follow - do you mean you'd prefer to have blank
squares for every space that has not yet been determined (rather than
the set of possible values) ? That would seem to me much less helpful
- but I'll try it and see how it looks.
Yes. In fact I copied the puzzle to Photoshop and erased all the
labels and printed the image. Maybe this would be a possible
preference?
I am interested in what algorithm is used under the "Auto" button.
>
Code is all there for you to look at :-)
But all it does is look at each square in turn, and if it already knows
that there is only a single value possible, then it removes that value
from the rest of the square's row,col and 3x3 square. It could repeat
that scan (very occasionally you can find a case where a square has been
already examined while multiple values were possible, and which reduces
to a single one, and is required to complete the puzzle) - but it
doesn't even do that.
I'll have to look at this again. It doesn't seem to complete all one
stage decisions. For example, after completing the Auto, it is clear
that the box in the second row, fifth column must be a 1. I suspect
my problem is that I don't understand the significance of the labels.
Life is full of things I don't understand.
> If you also enjoy Cryptogram puzzles, I have one which retrieves 4
quotes from the web every day and encodes them for your decoding
pleasure. It is my daily diagnostic tool to reveal the onset of
senility. You can take a look at:
go stack url
"http://home.infostations.net/jhurley/DailyCryptoquote.rev";
It's a 450k file. It contains a dictionary for a decoder utility.
Thanks Jim. I'll take a look at that - though I'm more likely to write a
stack to solve them than I am to do it myself.
I have not yet found any "puzzle" that is more challenging or
stimulating that programming.
I think this is what keeps many of us going.
Jim
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