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Hard 2/6/2006 Confused

 
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Adam
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PostPosted: Fri Feb 10, 2006 4:05 am    Post subject: Hard 2/6/2006 Confused Reply with quote
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
PostPosted: Fri Feb 10, 2006 6:55 am    Post subject: Reply with quote
(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
PostPosted: Fri Feb 10, 2006 7:09 am    Post subject: Reply with quote
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 so-called '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
PostPosted: Tue Feb 21, 2006 2:52 am    Post subject: Reply with quote
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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