FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in          Games  Calendar Log in to check your private messages    Is there a way to create "hard clues"?          Sudoku Programmers Forum Index -> Setting sudoku View previous topic :: View next topic   Author Message TriKri Joined: 30 Jul 2007 Posts: 5 : Items Posted: Tue Jul 31, 2007 5:18 pm    Post subject: Is there a way to create "hard clues"? Hello! I just wonder whether there exists efficient methods to a) create hard sudoku puzzles but with still many clues (hence "hard clues") b) create easy sudokus but with few clues? I have been thinking of searching for the clue which will require the most/less sophisticated methods to bring back after you have removed them ... but then it hit me that if you have to use a sophisticated method to get it back, there might still be other squares in which you can get a digit by using simpler methods, hence making the puzzle easier than what it seems like to the computer cause there is "other ways around". Does my method fall apart there? Back to top Ruud Site Admin Joined: 17 Sep 2005 Posts: 708 : Location: Netherlands Items Posted: Tue Jul 31, 2007 7:02 pm    Post subject: Here is a 38 clue minimal puzzle created by Ravel. It requires some very advanced solving techniques. Code: . . .|. . .|. . . . . 1|. 2 3|. 4 5 . 2 4|6 1 5|3 7 . -----+-----+----- . . .|. 8 2|7 . . . 1 8|5 . 7|. 6 . 2 . 7|1 . 6|8 5 . -----+-----+----- . 6 2|3 5 1|4 8 . . 8 .|. . .|. 3 . 1 . .|. . 8|. . 6 Here is a 17 clue Sudoku from Gordon's collection. You can solve it with singles only. Code: . . .|. . .|. 1 . 4 . .|. . .|. . . . 2 .|. . .|. . . -----+-----+----- . . .|. 5 .|4 . 7 . . 8|. . .|3 . . . . 1|. 9 .|. . . -----+-----+----- 3 . .|4 . .|2 . . . 5 .|1 . .|. . . . . .|8 . 6|. . . Ruud _________________ Meet me at sudocue.net Back to top TriKri Joined: 30 Jul 2007 Posts: 5 : Items Posted: Tue Jul 31, 2007 9:24 pm    Post subject: Okay ... I thought a 17 clues-sudoku was super hard to solve, since I thought they must have used some very advanced techniques to remove so many digits ... and super hard to find! However, I'm intrested in the techniques for finding those. Maybe they are classified... Back to top north55 Joined: 02 Dec 2006 Posts: 43 : Items Posted: Wed Aug 01, 2007 10:50 pm    Post subject: TriKri wrote: Okay ... I thought a 17 clues-sudoku was super hard to solve, since I thought they must have used some very advanced techniques to remove so many digits ... and super hard to find! However, I'm intrested in the techniques for finding those. Maybe they are classified... You will have to be pretty specific with a question to get an answer, I suspect. First of all some general facts. The number of givens has statistically no relation to how difficult to solve a puzzle is. Almost all puzzles of the total sudoku set are pretty easy. The average number of clues for a valid puzzle is around 26, allowing for minimal with symmetry. Almost all existing puzzles are computer generated. I know of no computer generator that can control the difficulty of a generated puzzle while generating, aside from not using some harder techniques. Two ways generated puzzles are filtered though... most allow you to pick a minimum difficulty, they throw away the ones too easy, and the generator has to have a solving technique strong enough to rate the hardest puzzle you intend to create. Back to top TriKri Joined: 30 Jul 2007 Posts: 5 : Items Posted: Thu Aug 02, 2007 12:07 pm    Post subject: Thanks! So there is no way to control the difficulty of a puzzle during generation, unless you wan't to get a puzzle as easy as possible? Okay. But what about templates? Is it some way to use templates to control the difficulty of the puzzle? I have heard about them but I don't know if the're used for that purpose. Back to top gsf Joined: 18 Aug 2005 Posts: 408 : Location: NJ USA Items Posted: Thu Aug 02, 2007 2:15 pm    Post subject: TriKri wrote: So there is no way to control the difficulty of a puzzle during generation, unless you wan't to get a puzzle as easy as possible? similar question over two threads ... there is rule of thumb for generating the hardest sudoku in a reply to you here but the hardest of those don't fall to any known non-guessing technique Back to top TriKri Joined: 30 Jul 2007 Posts: 5 : Items Posted: Thu Aug 02, 2007 6:43 pm    Post subject: Oops, sorry for that... ^_^; So guessing is allowed even for rated puzzles? It must be hard to judge those. Back to top merse Joined: 22 Dec 2009 Posts: 2 : Items Posted: Tue Dec 22, 2009 8:52 am    Post subject: If no method to create hard sudoku (just by random), than what is the distribution of hard sudokus? I know that the meaning of easy, medium, hard, very hard is not "easy" , but lets assume that we can mesure somehow, for example the mean level of some sudoku creator softwares, so after that what is the distribution? linear, power, logarithmic, exp? 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