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Re: Sudoku
Posted:
Aug 25, 2005 4:07 PM
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On Thu, 25 Aug 2005, Simon Tatham wrote:
[...]
> Hmm. I suppose it could be seen that way, although that's not how I
> saw it. I saw it as a special case of a rather different pattern,
> which I currently describe as `mutual neighbour analysis'. Rather
> than being a chain of arbitrary length, this pattern involves
> finding two non-adjacent squares and a bunch of their mutual
> neighbours, and observing that placing a particular number in one of
> the end squares forces all the neighbours to take values which cause
> a contradiction in the other end square.
[...]
> If the 45 square has a 4 in it, [...] a problem. Hence, the 45 square
> can't be a 4, so must be a 5.
Tell me again how this is distinct from "backtracking"? Basically,
your method is
1. Fill in a value for cell X.
2. Fill in a value for cells Y, Z,... dependent on X.
3. If at any point you find a contradiction, return to step 1.
That looks a lot like backtracking to me!
(Not that backtracking is bad; I just don't see why this particular
class of backtracking applications is interesting.)
-Arthur,
Sudoku is crosswording for the illiterate
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