FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in          Games  Calendar Log in to check your private messages    X-Colors Question          Sudoku Programmers Forum Index -> Programming sudoku View previous topic :: View next topic   Author Message Puzzler Joined: 04 May 2009 Posts: 36 : Items Posted: Tue May 19, 2009 1:55 pm    Post subject: X-Colors Question In the first example of X-Coloring on Sudopedia, the author indicates that the cell {R2,C8} is trapped, based on it's relationship with the cells marked 1 and 2. However, there appears to be another exception cell at {R8,C1}, but the author does not mention this one. Please could someone let me know if it also true that the cell {R8,C1} is an exception cell, or have I misunderstood the technique? [img]www.sudopedia.org/wiki/Image:XCEx1.png[/img] Back to top Lunatic Joined: 11 Mar 2007 Posts: 166 : Location: Ghent - Belgium Items Posted: Tue May 19, 2009 2:16 pm    Post subject: (EDITED: see next posts: dark red lines are wrong) The first X-Color example on Sudopedia is in fact an example of a Grouped X-Cycle. {R8,C1} is NOT an exception cell, however, it can recieve the GREEN color since it is conjugating with the BLUE cell at {R2,C1}. As a result of that cell {R8,C2} will loose candidate 2 as it can see both a GREEN and a BLUE colored cell. Why is {R8,C1} not an exception cell ? - it can not be part of a conjugating pair - not all other candidate cells within its house are peers of cells colored with the same color _________________ Marc ~~~<><~~~<><~~~<><~~~<><~~~ Last edited by Lunatic on Tue May 19, 2009 4:51 pm; edited 1 time in total Back to top daj95376 Joined: 05 Feb 2006 Posts: 349 : Items Posted: Tue May 19, 2009 4:27 pm    Post subject: Lunatic wrote: (EDITED) The first X-Color example on Sudopedia is in fact an example of a Grouped X-Cycle. {R8,C1} is NOT an exception cell, however, it can recieve the GREEN color since it is conjugating with the BLUE cell at {R2,C1}. As a result of that cell {R8,C2} will loose candidate 2 as it can see both a GREEN and a BLUE colored cell. Why is {R8,C1} not an exception cell ? - it can not be part of a conjugating pair - not all candidate cells within its house are peers of cells colored with the same color I believe that you have made a common mistake with X-Colors -- extending the logic too far. In step (2) of the Sudopedia description, conjugate cells are colored. Once you get to step (3), which is where [r2c1] gets colored, you can't color conjugates cells. Thus, cell [r8c1] can't be colored Green. That's the common mistake! Back to top Lunatic Joined: 11 Mar 2007 Posts: 166 : Location: Ghent - Belgium Items Posted: Tue May 19, 2009 4:48 pm    Post subject: daj95376 wrote: I believe that you have made a common mistake with X-Colors -- extending the logic too far. You're absolutely right (previous post edited) _________________ Marc ~~~<><~~~<><~~~<><~~~<><~~~ Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         Sudoku Programmers Forum Index -> Programming 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