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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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 Posted: Tue Jan 22, 2008 4:54 am Post subject: extreme #69, stuck |
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| Code: | . . 3 | . . 5 | . 6 .
. 9 . | . . . | . . 7
. . . | 7 . 3 | 1 . .
----------------------
. 3 . | . 6 . | 2 . .
2 . . | . 4 . | . . 8
. . 1 | . . . | . 9 .
----------------------
. . 9 | 1 . . | . . .
8 . . | . . . | . 4 .
. 7 . | 3 . . | 5 . . |
http://www.sudoku.org.uk/PrintWeeklySudoku.asp?number=69
stuck again, and where are the nice DP eliminations like before 
| Code: | 7 248 3 | 2489 1 5 | 489 6 249
1 9 2458 | 2468 28 268 | 348 2358 7
456 24568 24568 | 7 289 3 | 1 258 2459
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9 3 4578 | 58 6 178 | 2 157 145
2 56 567 | 59 4 179 | 367 1357 8
456 4568 1 | 258 3 278 | 467 9 456
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3 2456 9 | 1 57 2468 | 678 278 26
8 1 256 | 269 57 269 | 679 4 3
46 7 246 | 3 289 24689 | 5 128 1269 |
and just so everyone knows, I am posting these puzzles after the competition week is over as courtesy to the ongoing competition. |
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Asellus
Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
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| Posted: Tue Jan 22, 2008 2:16 pm Post subject: |
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storm_norm,
That is one tough puzzle. There is a Finned X-Wing in r34 that removes <4> from r2c3. But, that's about it for the ordinary methods.
I did an extensive "extended" Medusa that resulted in a wrap that (for all that work!) determined only that r5c4=9. But, that opened up a swordfish on <5> c149. And, after that, there was a {17} W-Wing in r45.
Then, it was back to more extended Medusa. There were various trap eliminations, some simplification, more trapping, and then finally a wrap that solved the puzzle. |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Tue Jan 22, 2008 9:17 pm Post subject: |
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I threw this puzzle into the "sudoku solver by logic" and it rated it at 5,000+...
to give a comparison, the very hard for 1/22/08 on this site was rated at 2,246
the hang up is that the solver doesn't see anything more complicated than x-wings. I am sure it doesn't see xy-wings, or coloring, or swordfish.
then it goes into guessing and I have noticed that the rating has a lot to do with how many guesses it will make. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Tue Jan 22, 2008 11:23 pm Post subject: |
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| Quote: | | then it goes into guessing and I have noticed that the rating has a lot to do with how many guesses it will make |
Counting the guesses that a computer program makes seems to me to be a long way from measuring the difficulty of the techniques a human could use to solve the puzzle.
Someone should measure how these rating schemes work on completely unsolved puzzles. I think they will fail, miserably.
A minimal Sudoku is one in which all the initial clues are required for a unique solution. You might think that, the fewer the clues, the more the unsolved candidates, the harder the puzzle. This is not true. Puzzles with a small number of initial clues tend to be relatively easy.
Keith |
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