Blackout Sudoku [Richards SVS]

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Is this suitable for a Sudoku competition?

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Total votes: 11

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Joined: Sun 29 Apr, 2012 2:21 pm

Blackout Sudoku [Richards SVS]

Post by Realshaggy » Wed 02 Jan, 2019 11:41 am

Rules: Place digits from 1 to 9 in the white cells such that each row, column and 3x3 box contains different digits.

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The example is taken from Richard's weekly Sudoku Variant Series from the puzzle portal of Logic Masters Germany. ... &id=0002NO

This type occurs semi-regulary at contests (probably I could have found one from a WSC if I had looked for it). In the interesting cases, the missing digit in a black square is different for the associated row, column and box. That means that the "solution" minus the black squares can not be extended to a latin square and that might be a reason to not consider it a sudoku variant.

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Re: Blackout Sudoku [Richards SVS]

Post by detuned » Wed 02 Jan, 2019 12:07 pm

This is a very interesting case where I’m not sure if I have a definite personal opinion about!

For classic sudoku, the requirement is that 1-9 appear everywhere exactly once. This is equivalently described as appears everywhere “at most once” - ie non repeating - or “at least once” - a less common interpretation, but the basis of the easiest solving heuristics.

I’m getting the impression that non-repeating is an important concept to the community because it extends very well to extra regions which aren’t of full size (eg in killer or renban groups). To this end, blackout remains consistent with an idea of non repeating.

Still, I have some sympathy with the dissenting point of view too. These don’t feel quite like sudoku because you don’t have the idea that each number must appear at least once in rows/columns/boxes. For years I’ve included the related variations of surplus and deficit on the online UKSC, but never at a size greater than 7x7 as I feel these only become less fun the bigger you make them.

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