The Godfather of Sudoku 47
circletimessquare writes "The New York Times profiles 55 year old Maki Kaji who runs Nikoli, in its article Inside Japan's Puzzle Palace. Nikoli is a puzzle publisher that prides itself on 'a kind of democratization of puzzle invention. The company itself does not actually create many new puzzles — an American invented an earlier version of sudoku, for example. Instead, Nikoli provides a forum for testing and perfecting them.' Also notable is how Mr. Kaji describes how he did not get the trademark for Sudoku in the United States before it was too late. But reminiscent of a theme many Slashdotters will find familiar about intellectual property: 'In hindsight, though, he now thinks that oversight was a brilliant mistake. The fact that no one controlled sudoku's intellectual property rights let the game's popularity grow unfettered, Mr. Kaji says.' Will Nikoli be the source of the next big puzzle fad after Sudoku?"
Nikolai (Score:5, Interesting)
Re:Sudoku Solvers (Score:2, Interesting)
It's a brute force algorithm using recursive functions on a 3D array. (It seemed like a good idea at the time) but it doesn't lend itself well to stopping halfway through as it can't declare any additional numbers are right until the puzzle is solved in it's entirety.
Unlike a logical approach which could solve Sudoku puzzle in a piecemeal fashion.
To half solve a puzzle and give the user the chance to restart again to prevent the server timing out the page would require transferring the original state, the current state and the information on how it got there.
The interesting thing is, on some test puzzles that were marked difficult it took remarkably few recursions to solve while some that were marked simple took a lot longer.
Re:Sudoku Solvers (Score:5, Interesting)
After you create the rules that will solve the puzzles you categorize the rules as easy, medium or hard.
Now if you want to create an easy puzzle you start randomly adding in (legal) numbers and each time you try to solve it using only the easy rules. The first time the solving part of the program solves the puzzle you are done. Alternatively you can start with a completed puzzle and remove a number and see if the number you removed is recoverable with the level of rules (easy, medium, hard) that you choose for the final puzzle.
Re:Sudoku Solvers (Score:4, Interesting)
My Perl sudoku solver was probably more complete - it even does set analysis: [A, B, C] are blank, values [2, 5, 7] are available, but A can only be [5, 7], B can only be [5, 7] so C must be 2.
It reverts to brute force only where its algorithms can't find any possible moves. I've only found that to be the case for puzzles with more than one legal solution (crappy cheap books).
Kakuro is more interesting - first the format is a cow to transcribe to a data file. I'm using "X Y DIRN LEN SUM" as the format. Output is a HTML file because plaintext doesn't quite read easily (my sudoku solver just outputs ASCII art).
The solver itself actually turned out to be very easy to write, and I get the feeling that it's not even complete yet (there are things I can do by hand that it doesn't attempt) and yet every puzzle I've thrown at it solves fine. It doesn't have a brute-force mode. I suspect this may be because either the kakuro book I'm using isn't very advanced, or it's just not so popular yet that people have crafted difficult puzzles.
What I'd really love to see is a standard data file format for describing these puzzles so I can share them and/or use other peoples' puzzles as input to my scripts. But I don't have THAT much free time, really...