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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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