permutation

gistfile1.rb

def permutations(array)
  n = array.length
  return [array] if n < 2
  rt = Array.new

  for i in 0...n
    ## Create a new array from [array] where the
    ## [i]-th term has been ignored.
    t = Array.new(array)
    t.delete_at(i)

    tz = permutations(t)
    tz.each do |tp|
      rt << tp.unshift(array[i])
    end
  end
  return rt
end