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Thread: Sudoku

  1. #1
    5 Star Lounger Ruff_Hi's Avatar
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    Sudoku

    Are these puzzles banned here? I got this one in an AA mag and I am pretty sure that you need to solve it by trial and error - I hate that, give me logic or give me death.
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    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

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  3. #2
    Plutonium Lounger
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    Re: Sudoku

    Why should they be banned?

    Solving a Sudoku puzzle is usually a mixture of logical reasoning and guessing...
    Don Wells posted a sudoku solver a few years ago, but it was lost in the server crash of last year.

    Added later: I found it in my archive - I've attached the zip file. I'm aware it's not the "logic" your seeking.
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  4. #3
    5 Star Lounger Ruff_Hi's Avatar
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    Re: Sudoku

    I thought you would get so many of these that you would get sick of them. I ran the solver and it solved it - true to its name. I looked at the code and it included a 'guess' routine. Disabling the guess routine gave a partial solution that is less solved than I got on my own (see below for where I am stuck).
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    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

  5. #4
    Plutonium Lounger
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    Re: Sudoku

    I don't think you can solve Sudoku puzzles solely by logical thinking, except perhaps for very simple ones (where you're given a lot of information). You can get only so far by reasoning, then you'll have to guess and try to continue reasoning from there, etc. If you find a contradiction, you'll have to backtrack and try again.

  6. #5
    5 Star Lounger Ruff_Hi's Avatar
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    Re: Sudoku

    I don't 100% agree with that statement. For me, the 'better' sudoku puzzles are ones that you can solve with logic, coupled with some 'estimates that lead to inconsistencies'. I don't mind those as long as they are only 3 or 4 chains long (ie you can do it in your head.

    Take the '6' in the top middle big square ... that has to be a 6 because ...

    1) the middle / middle big square's 6 must be in the center column, thus ruling out the center column for the top middle square
    2) the 6 in the top left big square rules out the 2nd row in the top middle big square
    3) the 6 mentioned in 2) also forces the 6 in the top left big square to the top row, thus ruling out the top row in the top middle big square

    I know that I can solve this puzzle by 'guessing' the value of 1 square (it is either a 3 or a 9), but if I put a 3 in that square, it requires 15 or so passes to come to an inconsistency. Not something that I can do in my head. I guess I don't want to fall back on the (as my prof use to say) 'brute force and stupidity' method.
    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

  7. #6
    Silver Lounger
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    Re: Sudoku

    There seems to be a logic to it to me. Much like an IF ... THEN or IF ... ELSE ... THEN or similar in various programming languages. I know in the simpler puzzles, the "it has to be this" is very easy to determine, but as they get harder, I switch from a case of "This square is X" to "This square can not be X,Y, or Z".
    Christopher Baldrey

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