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Thread: Sudoku creator

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    bob 6 is offline Java Rookie
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    Question Sudoku creator

    So I want to program Sudoku, but before I got to the programming, I realized that I didn't know how to make the original board. Sure, I could make my program start with a full board and hide some numbers, but I wouldn't know if it was solvable or not anymore. Is there a simple way to make a solvable beginning?

    Thanks in advance!

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    Jodokus is offline Senior Member
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    Default Re: Sudoku creator

    That must be easy, though I confess I didn't try.
    There are only four kinds of configuration for a board: illegal, solved (=legal and full), with one solution and with many solutions. I guess that you are interested in the kind with one solution and a minimal number of numbers already filled in.
    To recognize illegal and full must be trivial. To find one solution you use the algorithm of JosAH's blog on this forum:
    http://www.java-forums.org/blogs/josah/75-sudoku.html, and if you use more iterations until you find another solution it is in the many solutions category and so again you are not interested.
    So just write a genetic algorithm and reward one-solution solutions with a minimal filled-in-number-count and presto!
    No bug ever had to calculate its fitnessfunction.

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    quad64bit is offline Moderator
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    Default Re: Sudoku creator

    Is there a simple way to make a solvable beginning?
    I think I read somewhere that this is an NP-Hard problem, so, I don't think so.

    When I implemented one years back, I started with solved puzzles and then removed some random set of values. I had to test after each removal though, to ensure I didn't make the puzzle unsolvable. It was very iterative and guess & check, but computers are fast and great at this kind of thing. Puzzle generation still only took milliseconds.

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    bob 6 is offline Java Rookie
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    Default Re: Sudoku creator

    Thanks for the answers! It seems like you either solve it using the given formula or use guess and check. I won't use the formula until I fully understand it(I just skimmed through it) and guess and check isn't really my style. I think I'll first make an AI for Tic-Tac-Toe, and come back to this tomorrow with a fresh mind. Again, thanks for the quick answers.

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    Default Re: Sudoku creator

    Quote Originally Posted by bob 6 View Post
    Thanks for the answers! It seems like you either solve it using the given formula or use guess and check. I won't use the formula until I fully understand it(I just skimmed through it) and guess and check isn't really my style. I think I'll first make an AI for Tic-Tac-Toe, and come back to this tomorrow with a fresh mind. Again, thanks for the quick answers.
    What formula?

    kind regards,

    Jos

    ps. did you read my blog artice? All it does is use back tracking.
    The only person who got everything done by Friday was Robinson Crusoe.

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