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Apparently I don't understand coloring

 
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UmberGryphon

Joined: 05 Oct 2005
Posts: 8
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PostPosted: Tue Nov 01, 2005 10:22 pm    Post subject: Apparently I don't understand coloring Reply with quote

I'm trying to get my brain's wetware coloring algorithm up to the deductive level of Simple Sudoku's, but apparently I've pushed too hard, because now my algorithm tells me I can do things which lead to invalid moves.

For example, if the candidate 8s of the top 3 rows of a puzzle read:

Code:
..8|...|..8
8..|8..|...
8..|8..|8..


(1) I pick colors for the two 8s in the rightmost box

Code:
..8|...|..a
8..|8..|...
8..|8..|A..


(2) I deduce where the A must be in the middle box

Code:
..8|...|..a
8..|A..|...
8..|8..|A..


(3) I conclude where the 'a' must be in the middle box (since there are no other 8s in that column)

Code:
..8|...|..a
8..|A..|...
8..|a..|A..


(4) I attempt to claim that the 8 in the leftmost box can't be in the bottom row, which turns out to be wrong.

Where did I do something horribly wrong? Step 3? Step 2? Both? And could someone point me to a description of EXACTLY what one is allowed to do in coloring?

UmberGryphon
(who feels like a n00b for needing to ask)
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Ruud
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Joined: 17 Sep 2005
Posts: 708
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Location: Netherlands

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PostPosted: Wed Nov 02, 2005 12:10 am    Post subject: Reply with quote

Hi,

you can only apply color to conjugates, where there are 2 cells in a row/column or box:

Code:
..A|...|..a
B..|b..|...
8..|B..|A..

are the only colors you can apply, and there is no elimination possible based on these colors.

The flaw in your logic is in step (2). The (A) you add forms no conjugate pair with the existing (a). So you have to form a new chain, starting with (b).

There are very informative topics on this forum about coloring.

try: http://www.setbb.com/phpbb/viewtopic.php?t=311&mforum=sudoku
The explanations by Lummox JR are very clear.

Ruud.
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