From: Raf Coremans <rrafje@...>
Date: 2007-07-23T15:43:25+09:00
Subject: Re: array permutations

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2007/7/23, Alex Ciarlillo <ac251404@ohio.edu>:
>
> The other day I ran into a problem where I needed all the permutations
> of a given array. I knew I had covered this in some of my CS classes but
> couldn't come up with the algorithm at first. I figured it out on the
> drive home from work and decided to rubify it and add it as a method to
> the array class. This is what I came up with and was just wondering if
> anyone else had a cleaner or more effecient way of accomplishing this.
>
> class Array
>   def each_perm
>     if self.size == 1
>       yield self
>     else
>       self.each_index do |i|
>         tmp, e = self.dup, self[i]
>         tmp.delete_at(i)
>         tmp.each_perm do |x|
>           yield e.to_a + x
>         end
>       end
>     end
>   end
> end
>
>
> --AC
> --
> Posted via http://www.ruby-forum.com/.
>
>

There's a problem with the "to_a" in "yield e.to_a + x". It gets a lot of
"default `to_a' will be obsolete" warnings, and it gives the wrong result
for, for instance, [1, 2, 'a'..'z'].each_perm. I'd go with "yield [e] + x"
instead.

For the rest, looks OK to me.


Regards,
Raf

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