quick sorting method in Ruby

quick-sort.rb

def quicksort(array)

  def partition(array)
    pivot,left, right =array[0], [], []
    array[1..-1].each do |x| 
       x > pivot ? right << x : left << x
    end
     [left, pivot , right]
  end

  return array if array.size <= 1
  left, pivot , right = partition(array)
  res = quicksort(left) + [pivot] + quicksort(right)
  return res

end