FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in          Games  Calendar Log in to check your private messages    Forcing chains types          Sudoku Programmers Forum Index -> Solving sudoku View previous topic :: View next topic   Author Message gaby Joined: 02 Jul 2005 Posts: 120 : Items Posted: Thu Feb 02, 2006 5:56 pm    Post subject: Forcing chains types Hi, I've run across a few sample puzzles that don't quite work with my Unique Rectangles code. Am I right in thinking that type 1 unique rectangles can only appear as type A, and never as type B? This puzzle proved it to me: Code: 5--1-2--8 -2--3--1- 8-------6 78-396-54 9--527--1 26-814-73 3-------2 -4--6--3- 6--2-3--5 It got to here: Code: # 4 -> [r2,c1] One number possible in cell # 1 -> [r4,c3] One number possible in cell # 2 -> [r4,c7] One number possible in cell # 3 -> [r5,c2] One number possible in cell # 4 -> [r5,c3] One number possible in cell # 5 -> [r6,c3] One number possible in cell # 9 -> [r6,c7] One number possible in cell # 1 -> [r8,c1] One number possible in cell # 1 -> [r3,c2] Candidate appears once in c2 # 5 -> [r7,c2] Candidate appears once in c2 # 2 -> [r8,c3] Candidate appears once in c3 # 6 -> [r2,c4] Candidate appears once in c4 # 6 -> [r1,c3] Candidate appears once in c3 # 3 -> [r3,c3] Candidate appears once in c3 # 5 -> [r3,c5] Candidate appears once in c5 # 9 -> [r3,c6] One number possible in cell # 8 -> [r2,c6] One number possible in cell # 1 -> [r7,c6] One number possible in cell # 5 -> [r8,c6] One number possible in cell # 3 -> [r1,c7] Candidate appears once in c7 # 5 -> [r2,c7] Candidate appears once in c7 # 1 -> [r9,c7] Candidate appears once in c7 # 2 -> [r3,c8] Candidate appears once in c8 # 8 -> [r8,c7] Candidate appears once in r8 # 6 -> [r5,c7] One number possible in cell # 8 -> [r5,c8] One number possible in cell # 6 -> [r7,c8] Candidate appears once in c8 # 4 <- [r7,c5] X-Wing in 4's: c4, c7 # 9 <- [r9,c3] X-Wing in 9's: c2, c8 Then suggested this: Code: Unique Rectangle: A = [r3,c4], B = [r3,c7], C = [r7,c4], D = [r7,c7] Candidate nums: A = {4,7}, B = {4,7}, C = {4,7,9}, D = {4,7} Unique rectangle, A = [r3,c4], B = [r3,c7], C = [r7,c4], D = [r7,c7]. Type 1, cell C has extra numbers # 4 <- [r7,c4] Unique rectangle, A = [r3,c4], B = [r3,c7], C = [r7,c4], D = [r7,c7]. Type 1, cell C has extra numbers # 7 <- [r7,c4] Unique rectangle, A = [r3,c4], B = [r3,c7], C = [r7,c4], D = [r7,c7]. Type 1, cell C has extra numbers The rectangle it suggested fit type 1, layout B. Is this legitimate? Gaby _________________ Free daily sudoku - Online puzzle database http://vanhegan.net/sudoku/ Back to top Carcul Joined: 29 Dec 2005 Posts: 50 : Location: Coimbra, Portugal Items Posted: Thu Feb 02, 2006 7:01 pm    Post subject: Hi Gaby. A type-1 unique rectangle is defined as four cells, distributed by exactly two boxes, two rows, and two columns, and all populated by the same two candidates "x" and "y", except just one of them that, besides "x" and "y", is also populated by one or more other candidates: is this cell, we can thus eliminate "x" and "y". So, it does not make sense to consider type 1A or 1B. BTW, your puzzle does not "need" any unique rectangle to be solved. Hope this help. Regards, Carcul Back to top gaby Joined: 02 Jul 2005 Posts: 120 : Items Posted: Thu Feb 02, 2006 7:11 pm    Post subject: I read about it a bit more in Trebor's PDF file about it, and I had missed out the constraint about the number of boxes that it has to span. When this is applied it solves the puzzles properly, without error. If you do let four cells span four boxes, you might as well call it a forcing chain. Gaby _________________ Free daily sudoku - Online puzzle database http://vanhegan.net/sudoku/ 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