Help to find puzzle

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Help to find puzzle

Postby m_b_metcalf » Wed Jul 02, 2014 1:49 pm

There exists a puzzle with 20-odd givens based on the MC grid
Code: Select all
1  2  3  4  5  6  7  8  9
4  5  6  7  8  9  1  2  3
7  8  9  1  2  3  4  5  6
2  3  4  5  6  7  8  9  1
5  6  7  8  9  1  2  3  4
8  9  1  2  3  4  5  6  7
3  4  5  6  7  8  9  1  2
6  7  8  9  1  2  3  4  5
9  1  2  3  4  5  6  7  8

(or its version with n=10-n), but I cannot find it anywhere. Does someone please have it on file or know of a link?

Many thanks,

Mike Metcalf
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Re: Help to find puzzle

Postby eleven » Wed Jul 02, 2014 8:01 pm

Not sure what you are looking for.
Maybe this post could be a help ?
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Re: Help to find puzzle

Postby coloin » Wed Jul 02, 2014 11:32 pm

m_b_metcalf wrote:There exists a puzzle with 20-odd givens based on the MC grid .......

well its based on the MC grid - in that it has 6 repeating minirows - but I dont think it the MC grid
im not sure how many grids have all 6 bands less than 30/416.

im sure "checker" or "gridchecker" would confirm the no 19.

C
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Re: Help to find puzzle

Postby m_b_metcalf » Thu Jul 03, 2014 7:50 am

Sorry, I should have been more explicit. The grid starts

Code: Select all
9 8 7 6 5 4 3 2 1
3 2 1 9 8 7 6 5 4

(n=10-n) and the puzzle starts
Code: Select all
. . . . . . . . .
. . . . . . . . 4

It's an absolute worst-case puzzle for a naive brute-force solver. I recall finding it on sudopedia but can't find it on its mirror.

Regards,

Mike
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Re: Help to find puzzle

Postby tarek » Thu Jul 03, 2014 10:56 am

Hi Mike,

Wouldn't a 10-n version of the MC grid suffice??

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Re: Help to find puzzle

Postby eleven » Thu Jul 03, 2014 7:04 pm

For me the internet was much better 15 years ago, when the fools did not have the tools to spoil it with their rubbish.

Now it's probably impossible to find, what you want, though we can be sure, that it is still published somewhere.
All the links to "worst case" puzzles for backtracking solvers go to this 17 clue, which has been in the wikipedia.
Code: Select all
. . . . . . . . .
. . . . . 3 . 8 5
. . 1 . 2 . . . .
. . . 5 . 7 . . .
. . 4 . . . 1 . .
. 9 . . . . . . .
5 . . . . . . 7 3
. . 2 . 1 . . . .
. . . . 4 . . . 9
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Re: Help to find puzzle

Postby m_b_metcalf » Fri Jul 04, 2014 7:15 am

eleven,
Thanks. That's perfect. I'm in discussion with the author of a brute-force code. It takes 61s to solve this puzzle. By replacing n by 10-n the time falls to 0.1s! (Of course, in real life, no solver is actually necessary as it is completely solvable with singles only.)

Regards,

Mike
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