From: Alex Ciarlillo <ac251404@...>
Date: 2007-07-23T13:52:08+09:00
Subject: array permutations

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
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