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keith
Joined: 19 Sep 2005 Posts: 3355 Location: near Detroit, Michigan, USA
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Posted: Sat Aug 11, 2007 9:25 pm Post subject: An Easy 17-clue Puzzle |
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By Sam's definition, this one is very easy:
Code: | 0 8 0 0 0 0 0 0 9
0 1 2 0 0 0 0 0 0
0 0 0 6 0 0 3 0 0
0 7 0 0 0 0 2 8 0
9 0 0 4 0 0 0 0 0
0 0 0 3 0 0 0 0 0
3 0 0 0 0 0 4 0 0
5 0 0 0 8 0 0 0 0
0 0 0 0 1 0 0 0 0 | Keith |
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Marty R.
Joined: 12 Feb 2006 Posts: 5770 Location: Rochester, NY, USA
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Posted: Sun Aug 12, 2007 11:52 pm Post subject: |
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Quote: | By Sam's definition, this one is very easy: |
I don't know what factors Sam uses in assigning a grade. But I have seen puzzles from various sources graded Easy, Medium, Hard, or whatever, which require nothing more than subsets and locked candidates. That's all that's required with this one, but I'd consider it harder than some others because of the small number of givens and, thus, the greater number of pencil marks required. With all those candidates, it's easier to make a mechanical error. |
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Asellus
Joined: 05 Jun 2007 Posts: 865 Location: Sonoma County, CA, USA
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Posted: Mon Aug 13, 2007 8:03 pm Post subject: |
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Marty R. wrote: | I'd consider it harder than some others because of the small number of givens and, thus, the greater number of pencil marks required. |
On the other hand...
I don't start with pencil marks. Out of laziness, I first scan puzzles for obvious placements. For instance, it is obvious that R1C3 and then R5C2 are <3>. It is almost as obvious that R2C4 and R3C9 are <8>. The number of cells requiring pencil marks are reduced already: so much unnecessary pencil mark exertion avoided! However, the obvious placements are not done yet.
How far one can get with such placements will vary for different folks. But practicing this approach increases what becomes "obvious." In the case of this puzzle, I found it fairly easy to complete the entire thing in a few minutes without making a single pencil mark. In my book, that ranks it as Easy indeed. |
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Marty R.
Joined: 12 Feb 2006 Posts: 5770 Location: Rochester, NY, USA
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Posted: Mon Aug 13, 2007 9:12 pm Post subject: |
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I just check each band and stack to see if a number is placeable in the 3rd box when it's already present in two boxes. After that I start right in with pencil marks. I could do more checking for obvious placements and maybe will try. But right now I don't know the tradeoff between fewer pencil marks versus extra time looking for placements. |
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keith
Joined: 19 Sep 2005 Posts: 3355 Location: near Detroit, Michigan, USA
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Posted: Mon Aug 13, 2007 10:00 pm Post subject: |
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Actually, all this one requires is singles. "Very Easy", except the paucity of initial clues makes it harder, I think.
Keith |
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Steve R
Joined: 24 Oct 2005 Posts: 289 Location: Birmingham, England
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Posted: Mon Aug 13, 2007 11:51 pm Post subject: |
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Maybe. At the same time, while there is no general connexion between difficulty and the number of clues, I don’t think this is true for minimal puzzles.
The huge majority of the minimal 17s are very easy. The average Sudoku Explainer rating is probably about 1. By contrast the minimal 38s have an average rating of 7.5.
Admittedly only 952 minimal 38s are known at present – Håvard Graff had a spell with his supercomputer and found another 951 – but it seems plausible that, when a puzzle requires as many as 38 clues to offer a unique solution, the clues must have a tendency not to interact very strongly.
Of course, “not to interact very strongly” is waiting for a precise definition….
Steve |
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