Sudoku Py / C++11 / D?

[Era Scarecrow]

On Saturday, 25 August 2012 at 00:51:23 UTC, Chris Cain wrote:
> On Friday, 24 August 2012 at 23:14:02 UTC, maarten van damme 
> wrote:
>> http://en.wikipedia.org/wiki/File:Sudoku_puzzle_hard_for_brute_force.jpg
>
> It occurs to me that one of the main reasons why this 
> particular puzzle would be hard for brute force is that the 
> first line is blank and more than half of the second line is 
> blank, and it seems like it is designed to have as many choices 
> as possible before a set square is encountered.
>
> I bet it could be solved much quicker by a computer by doing it 
> in reverse.

  Is most likely. What would you do, have multiple threads all 
solving it until one came with the fastest solution and then fix 
it back to how it should be? It would work...

  As a test I've taken the puzzle and converted it, normally I 
gave it up after some 30 seconds but flipped it was 2 seconds.

As the picture puzzle shows:
..............3.85..1.2.......5.7.....4...1...9.......5......73..2.1........4...9

Flipped:
....4...9..2.1....5......73.9.........4...1.....5.7.....1.2.........3.85.........

  Strange, flipping it various ways and connecting them comes up 
with an interesting patterns.

> I've got some ideas, maybe I'll write a solution to this 
> myself. :)

  Adding another level of possibilities removal before going to 
brute force can definitely do a lot.


On Saturday, 25 August 2012 at 01:00:04 UTC, Timon Gehr wrote:
> FWIW both mine and Maarten's solution require a trivial amount 
> of time to solve it.

  Same for my C version of the solver. But that's not really the 
topic here :P