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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 17, 2011 4:36 PM
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Mike Terry wrote:

>"Rock Brentwood" <> wrote in message

>>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've never come across a sudoku variant where part of the objective was to
>prove the solution is unique. In contrast, many sudoku puzzles actually
>state up front that the solutions are unique as one of the puzzle
>constraints, and the ones that don't do this *are* in fact always unique,
>i.e. they have just made the constraint a "secret rule" of the puzzle

It's no secret. But if there is not a unique solution, the solver by
necessity gets to a point where the "next step" is no longer logically
implied by the structure of the puzzle. That is, you have several
equally valid guesses, all of which lead to a solution. That defeats
the whole purpose of the puzzle.

Stephen J. Herschkorn
Math Tutor on the Internet and in Central New Jersey and Manhattan

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