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Topic: sudoku, again
Replies: 34   Last Post: Sep 24, 2011 8:41 PM

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Stephen J. Herschkorn

Posts: 2,297
Registered: 1/29/05
Re: sudoku, again
Posted: Sep 22, 2011 1:09 PM
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Andrew B wrote:

> On 21/09/2011 21:00, RichD wrote:

>> On Sep 20, Willem<wil...@toad.stack.nl> wrote:

>>> )> >>>The REAL issue is that to solve a Sudoku grid, there are
>>> actually TWO
>>> )> >>>parts: (a) find a solution (i.e. prove that one
>>> )> >>>exists), but also (b)prove that it is the ONLY
>>> )> >>>solution.
>>> )>
>>> )> I have done sudoku puzzles in which I have gotten
>>> )> to a point from which I could produce two
>>> )> solutions.
>>> )
>>> ) What is the smallest number of initially
>>> ) fixed cells such that the solution is
>>> ) guaranteed unique?
>>> 78, I think. Or 17. I'm not sure what you wanted to ask exactly.

>> It's a bit tricky to phrase precisely, though a simpe question.
>> What is the smallest number of initially determined cells,
>> such that there is at least one puzzle of such configuration,
>> with a unique solution?
>> And you claim there is a known example of 17?

> http://mapleta.maths.uwa.edu.au/~gordon/sudokumin.php claims to list
> about 50,000 known examples.

I remember hearing long ago that, empirically, 17 was the smallest
number amogst sudokus prodcued to date. Has it actually been proven
that there can be no fewer than 17?

Stephen J. Herschkorn sjherschko@netscape.net
Math Tutor on the Internet and in Central New Jersey and Manhattan

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