Shuffle cards in place

fisher_yates_shuffle.rb

# randomly shuffle cards in-place
# Fisher-Yates Shuffle
# Use the back of the array for storing the
# randomly picked card and move your way to the front
class Array
  def shuffle
    length = self.size
    array = self.dup

    (length - 1).step(0, -1).each do |i|
      random_index          = rand(i+1)
      tmp                   = array[i]
      array[i]              = array[random_index]
      array[random_index]   = tmp
    end
    array
  end
end

a = (0...52).to_a
puts a.inspect
puts a.shuffle.inspect