Sudoku Py / C++11 / D?

[Era Scarecrow]

On Monday, 20 August 2012 at 20:43:54 UTC, maarten van damme 
wrote:
> Yes, but these techniques have a drawback : they are not 
> guaranteed to find solutions yet they are guaranteed to 
> increase the time a run takes.

  The extra time it takes via a planned route rather than brute 
forcing is well worth the effort. Besides, they mostly make it 
more possible for the one-one-possible matches to be found much 
faster and safely.

  In my tests with the C version (that was written 6 years ago?) 
each time I added an extra algorithmn to remove dead 
possibilities, it sped the code up by a factor of 3 or more.

> I'm still unsure if it would be worth carrying over that 
> possibilities array. I'm going to implement auto-solving of 
> single candidates and see how big the performance hit/gain is.

> Yes but I only test allowed numbers so if of those 20 
> combinations we need 5 fours, 3 nines, 4 twos and 8 ones, the 
> possibilities to test are only 3491888400 which is reasonable 
> for a pc :)

  Indeed. My code only does that too, but it's still alot of 
possibilities.

> That is indeed a really smart approach, I'll try that.
>
> By optimizing a bit more (who would've thought that a for loop 
> copying values one by one is way faster then some slice magic?) 
> I was able to make my program 3 times faster. Now it can solve 
> an empty sudoku in 0.05 ms and solve the hard sudoku in 0.06s. 
> My sudoku generator for valid sudoku solution now runs at 13000 
> sudokus a second.

  Was that sarcasm? My own code only uses copying when it's 
working in the next section of brute force, otherwise it's all 
referenced.

> And vera, why are you using exceptions instead of return 
> values? I think it's slowing your solver down considerably.

  I only use exceptions twice and both when it would be unable to 
find a solution; I suppose I can try putting nothrow on 
everything and return a bool if it had an error for solving, or 
when it had to, inside a structure. Mmmm... I'll give it a try.

  This is actually one of the first time's I'm actually using 
exceptions.