

Show HN: NQueens problem solved using backtracking in Elixir lang - tacticiankerala
https://github.com/tacticiankerala/N-Queens

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taeric
It would be interesting to see timing results of this implementation.
Similarly, comparisons to other implementations/algorithms. I will have to
fire up erlang when I get home this evening.

I am basically a broken record on this topic, but I do like sending more
people to see the Dancing Links algorithms solving this (and other related
problems, such as sudoku.)[1] The techniques in DLX cut the search space for
the 8-queens down to just 1,048 board states. (For 13, the number of boards is
up to 1,046,318)

[1]
[http://taeric.github.io/DancingLinks.html](http://taeric.github.io/DancingLinks.html)

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tacticiankerala
8-queens : 0.19s user 0.09s system 127% cpu 0.222 total

12-queens : 0.21s user 0.11s system 129% cpu 0.244 total

16-queens : 0.29s user 0.10s system 119% cpu 0.325 total

20-queens : 2.79s user 0.10s system 102% cpu 2.826 total

24-queens : 7.50s user 0.10s system 100% cpu 7.533 total

Thanks a lot for sharing the Dancing links algorithm. It looks really
interesting. I wanted to try sudoku with backtracking,but now I would like to
give dancing link a try!

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taeric
Are those times for finding a solution, or for all solutions? If all, that is
truly impressive!

Dancing links is a backtracking algorithm, just a nice way to optimize the
backtracking.

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tacticiankerala
It is for finding the first solution. Sorry that I didn't mention it.

~~~
taeric
No worries. I could have guessed, if I'd paid attention to how large of an N
you looked at. :)

Also, I should explicitly say thanks for sharing! It is fun reading solutions
to this puzzle. Also fun to read Erlang.

------
HugoDias
A solution for doing the same thing in Ruby:
[https://gist.github.com/hugodias/cf89ba138b986ddb3e7d](https://gist.github.com/hugodias/cf89ba138b986ddb3e7d)

Time spent processing for 12 queens: 3.59 seconds

~~~
tacticiankerala
Here is the benchmarking for 12-queens

12-queens : 0.21s user 0.11s system 129% cpu 0.244 total

But, I see that you are finding all the solution. My program only finds the
first solution.

