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Adam Guest

Posted: Fri Feb 10, 2006 4:05 am Post subject: Hard 2/6/2006 Confused 


Hey Guys
Hope you can help me understand why this is the next move. Here's the puzzle
Code:  _ 1 _ 6 3 8 9 _ X
3 4 9 5 7 2 6 1 8
8 5 6 4 9 1 7 3 2
_ 6 _ _ 4 5 3 _ 1
5 9 _ 7 _ 3 _ _ _
4 3 _ _ 2 _ 5 8 _
9 7 5 3 _ _ _ _ _
_ 2 4 _ 5 7 _ _ 3
_ 8 3 2 _ _ _ _ _ 
Apparently the X is a 5. WHY!? What rule is this and can you explain how this rule works? I see that there's a pair rule, if that's in fact what allows you to get this number, can someone explain to me how this rule works? Thanks :)
Adam 

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tcdev
Joined: 09 Feb 2006 Posts: 5 Location: Sydney, Australia

Posted: Fri Feb 10, 2006 6:55 am Post subject: 


(X) is either (4/5)
Pair R5C9 & R7C9 (4/6)
So (X) cannot be 4, it must be 5.
Regards,
Mark 

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tcdev
Joined: 09 Feb 2006 Posts: 5 Location: Sydney, Australia

Posted: Fri Feb 10, 2006 7:09 am Post subject: 


I should probably explain... (I'm a newbie so please excuse my lack of proper sudoku lingo)
The 'Pairs Rule' as I understand it...
If you have 2 pairs in any row, column or 3X3 box, then no other square in that row/column/box can have either of those two numbers.
In your case, since there is a pair (4/6) in column 9, no other square in that column can be either 4 or 6.
Similarly, if you have 2 numbers that exist in only (the same) 2 squares in any given row, column or box, then you can eliminate any other candidate numbers in those two squares (leaving just the socalled 'pairs').
You can also extend this to triplets (3 squares) as well.
Regards,
Mark 

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alanr555
Joined: 01 Aug 2005 Posts: 198 Location: Bideford Devon EX39

Posted: Tue Feb 21, 2006 2:52 am Post subject: 


Code: 
This puzzle can be solved using Mandatory Pairs  although it proved
useful to have the "missing" profiles for the rows and columns.
Congruent subsets included:
Row 1: 27 and 45
row 5: 18 and 246.
Col 1: 16 and 257
In any event a solution was derived without recourse to deriving
the candidate profiles.
Alan Rayner BS23 2QT



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