gistfile1.rb

#!/usr/bin/env ruby

require 'benchmark'

def permute(chars)
  if chars.length <= 1
    [chars]
  else
    result = []
    chars.each_with_index do |char, idx|
      remainder = chars[0...idx] + chars[idx+1..chars.length]
      permute(remainder).each do |permutation|
        result << [char] + permutation
      end
    end
    result
  end
end

puts Benchmark.measure { puts permute("abcdefghijk".chars.to_a).length }