## Help to find puzzle

Everything about Sudoku that doesn't fit in one of the other sections

### Help to find puzzle

There exists a puzzle with 20-odd givens based on the MC grid
Code: Select all
`1  2  3  4  5  6  7  8  94  5  6  7  8  9  1  2  37  8  9  1  2  3  4  5  62  3  4  5  6  7  8  9  15  6  7  8  9  1  2  3  48  9  1  2  3  4  5  6  73  4  5  6  7  8  9  1  26  7  8  9  1  2  3  4  59  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

m_b_metcalf
2017 Supporter

Posts: 9384
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Location: Berlin

### Re: Help to find puzzle

Not sure what you are looking for.
Maybe this post could be a help ?
eleven

Posts: 1903
Joined: 10 February 2008

### Re: Help to find puzzle

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
coloin

Posts: 1738
Joined: 05 May 2005

### Re: Help to find puzzle

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

Code: Select all
`9 8 7 6 5 4 3 2 13 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

m_b_metcalf
2017 Supporter

Posts: 9384
Joined: 15 May 2006
Location: Berlin

### Re: Help to find puzzle

Hi Mike,

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

Tarek

tarek

Posts: 2756
Joined: 05 January 2006

### Re: Help to find puzzle

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`
eleven

Posts: 1903
Joined: 10 February 2008

### Re: Help to find puzzle

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

m_b_metcalf
2017 Supporter

Posts: 9384
Joined: 15 May 2006
Location: Berlin