X-sudoku with only 4 (or 3) rows

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X-sudoku with only 4 (or 3) rows

Postby m_b_metcalf » Tue Jan 14, 2014 9:41 am

There was once a thread (in 2010?) on this topic, which was perhaps lost following the Forum crash. So, just for the record, here is an example:
Code: Select all
 . 3 1 6 . 8 9 5 .
 9 . 2 7 . 1 3 . 8
 8 7 . 3 . 4 . 6 1
 2 4 3 . 1 . 6 7 5
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .
 . . . . . . . . .   X-sudoku, four rows, symmetric, very hard

But ones with three rows also exist:
Code: Select all
 . . . . . . . . .
 . 5 6 9 . 8 1 . 2
 . . . . . . . . .
 . . . . . . . . .
 . 6 5 2 . 9 4 1 3
 . . . . . . . . .
 . . . . . . . . .
 . . 1 8 4 5 3 . 6
 . . . . . . . . .   X-sudoku, three rows, minimal, hard

Other shapes are possible with X that standard puzzles don't allow:
Code: Select all
 . 8 . 1 . 2 4 6 .
 . . . . . . . . 2
 5 . . . . . . . 8
 2 . . . . . . . 9
 . . . . . . . . .
 9 . . . . . . . 4
 6 . . . . . . . 1
 7 . . . . . . . .
 . 1 2 6 . 3 . 8 .   x-sudoku, empty box, symmetric, hard


and a smaller box (but maybe that's possible with standard puzzles too):
Code: Select all
 . . . . . . . . .
 . 7 4 9 . 8 6 2 .
 . 3 . . . . . 1 .
 . 2 . . . . . 7 .
 . 6 . . . . . 3 .
 . 1 . . . . . 4 .
 . 4 . . . . . 6 .
 . . 6 5 1 4 3 . .
 . . . . . . . . .   x-sudoku, symmetric, minimal, hard


I'm happy to try other interesting shapes that folks might propose.

Regards,

Mike Metcalf
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Re: X-sudoku with only 4 (or 3) rows

Postby enxio27 » Tue Jan 14, 2014 3:11 pm

Interesting! Wondering just how "hard" these are--what is the most difficult technique required for these?
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Re: X-sudoku with only 4 (or 3) rows

Postby m_b_metcalf » Tue Jan 14, 2014 3:38 pm

enxio27 wrote:Interesting! Wondering just how "hard" these are--what is the most difficult technique required for these?

'Hard' corresponds to SE ~8.5 - ~9.5, 'very hard' to SE >~9.5.

M.
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