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Scanning vs Cross Hatching

 
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gindaani



Joined: 06 Mar 2009
Posts: 79
PostPosted: Thu Apr 04, 2013 4:15 pm    Post subject: Scanning vs Cross Hatching Reply with quote
I was looking at the basic techniques on the Sudopedia mirror to put names to the techniques I use. I don't really understand how Scanning is different from Cross Hatching. There seems to be an implication that Scanning is somehow better, but I see no difference.

http://sudopedia.enjoysudoku.com/Scanning.html

Can anyone explain the difference?
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sun Apr 07, 2013 8:00 am    Post subject: Re: Scanning vs Cross Hatching Reply with quote
gindaani wrote:
I was looking at the basic techniques on the Sudopedia mirror to put names to the techniques I use. I don't really understand how Scanning is different from Cross Hatching. There seems to be an implication that Scanning is somehow better, but I see no difference.

http://sudopedia.enjoysudoku.com/Scanning.html

Can anyone explain the difference?

I can't explain the difference. I suppose they are both things that I do, though I have never tried to explain them as algorithms.

I solve puzzles, as best I can, with pencil and paper, without pencil marks.

I start by scanning each floor of 3 rows to see where digits might be placed. Then, I scan each tower of three columns. But, with each tower, I am also looking at the intersecting floors. Then, I look at each digit in turn, to visualize how its pattern of unknowns fits in the puzzle.

In doing so, I have a theorem that quickly excludes candidates that cannot have single-digit eliminations from patterns like X-wings, kites or skyscrapers.

I tried to explain it once, and found no interest. Except Danny said, he knew that but had forgotten it!

Only then do I start looking at each row, column, and block for each digit 1-9.

Keith
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