FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in          Games  Calendar Log in to check your private messages    Is this a BUG?          Sudoku Programmers Forum Index -> Solving sudoku View previous topic :: View next topic   Author Message Ruud Site Admin Joined: 17 Sep 2005 Posts: 708 : Location: Netherlands Items Posted: Thu Dec 29, 2005 7:37 pm    Post subject: Is this a BUG? Hi, I know this discussion has largely been held on the players forum, but most participants also visit this forum, so here is my question: I found the following Sudoku while I was generating new ones with both horizontal and vertical symmetry: Code: . 5 .|. . .|. 4 . . . 1|. 9 .|8 . . 2 7 .|. . .|. 1 6 -----+-----+----- . . .|5 . 8|. . . 8 . .|. . .|. . 2 . . .|7 . 4|. . . -----+-----+----- 4 6 .|. . .|. 3 5 . . 7|. 3 .|4 . . . 3 .|. . .|. 9 . After a very easy opening, this sudoku requires crowbar techniques. When I tested a candidate, it came to his pattern: Code: .------------.------------.------------. | 69  5   69 | 8   7   1  | 2   4   3  | | 3   4   1  | 26  9   26 | 8   5   7  | | 2   7   8  | 34  45  35 | 9   1   6  | :------------+------------+------------: | 7   9   3  | 5   2   8  | 1   6   4  | | 8   1   4  | 39  6   39 | 5   7   2  | | 56  2   56 | 7   1   4  | 3   8   9  | :------------+------------+------------: | 4   6   29 | 1   8   29 | 7   3   5  | | 59  8   7  | 69  3   569| 4   2   1  | | 1   3   25 | 24  45  7  | 6   9   8  | '------------'------------'------------' I noticed that there is only one cell with 3 candidates left. This reminded me of the Bivalue Universal Grave (BUG) discussion I've seen on the players forum. I have a few questions, before coding this into Sudo Cue: When this happens (all unbound cells have 2 candidates except one with 3 candidates), is it always a BUG situation, or do I need to perform additional tests? In this case, candidate 9 in R8C6 does solve the Sudoku. I read I can pick it because it has 3 entries in cel, row, column and box. Is this always the case, or are there also other variations of the BUG pattern? Ruud. _________________ Meet me at sudocue.net Back to top Carcul Joined: 29 Dec 2005 Posts: 50 : Location: Coimbra, Portugal Items Posted: Thu Dec 29, 2005 9:27 pm    Post subject: Hi Ruud. When you have a grid with all non assigned cells with two candidates, except one with three candidates, you can always immediatly apply the BUG principle. This is the most simple application of the BUG principle. However, there are other variations, for example in a grid with more than one cell with three candidates or even one (or more) cells with four candidates. You can see these examples in the players forum in the thread entitled "The BUG principle". Regards, Carcul Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         Sudoku Programmers Forum Index -> Solving sudoku All times are GMT Page 1 of 1   Jump to: Select a forum Sudoku----------------Solving sudokuSetting sudokuProgramming sudokuThe mathematics of sudokuExotic sudoku Library----------------PuzzlesSoftwareSudoku elsewhere Not sudoku----------------Random thoughtsForum feedback  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum   Powered by phpBB © 2001, 2005 phpBB Group Igloo Theme Version 1.0 :: Created By: Andrew Charron