Sudoku Programmers Forum Index

 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister   ProfileProfile   Log inLog in          Games  Calendar

Log in to check your private messagesLog in to check your private messages   

Criteria for Unique Solution

 
Post new topic   Reply to topic    Sudoku Programmers Forum Index -> Solving sudoku
View previous topic :: View next topic  
Author Message
King Wonka

Joined: 14 Dec 2005
Posts: 26
:

Items
PostPosted: Wed Dec 21, 2005 2:46 pm    Post subject: Criteria for Unique Solution Reply with quote

Was wondering the best way to test for uniqueness. My understanding is to just select a random cell and if more than 1 number is a viable answer then this sudoku is not unique. Is it that simple?

If that is so, randomizing the numbers in a sudoku only acts to give the human solver some variation. And the uniqueness is created by selecting certain numbers to remove as long as the numbers removed don't create multiple solutions. Is this correct?
Back to top
View user's profile Send private message
Ruud
Site Admin
Joined: 17 Sep 2005
Posts: 708
:
Location: Netherlands

Items
PostPosted: Wed Dec 21, 2005 3:26 pm    Post subject: Reply with quote

Hi Anthony,

Uniqueness is usually checked by a backtracking technique, like Dancing Links. This is because a non-unique Sudoku may have 77 solved cells, and only 4 unsolved with 2 possibilities to complete it.

Checking only a random single cell will only tell you that cell has only one option, but it does not tell you anything about the other 80 cells.

However, if you only want to prove non-uniqueness, testing a single cell can tell you that, because if it allows multiple digits, you know the puzzle has multiple solutions.

Ruud.
_________________
Meet me at sudocue.net
Back to top
View user's profile Send private message Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    Sudoku Programmers Forum Index -> Solving sudoku All times are GMT
Page 1 of 1

 
Jump to:  
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
Sudoku Programmers topic RSS feed 


Powered by phpBB © 2001, 2005 phpBB Group

Igloo Theme Version 1.0 :: Created By: Andrew Charron