O(n*log n) sorting algorithms: Quicksort and Mergesort. Implemented in Ruby

mergesort.rb

module Mergesort
  def self.sort(array)
    return array if array.length <= 1
    middle = array.length/2
    left = sort(array[0..(middle-1)])
    right = sort(array[middle..-1])

    merge(left, right)
  end

  def self.merge(left, right)
    result = []
    while(left.length > 0 || right.length > 0) do
      if left.length > 0 && right.length > 0
        if left.first <= right.first
          result << left.shift
        else
          result << right.shift
        end
      elsif left.length > 0
        result << left.shift
      elsif right.length > 0
        result << right.shift
      end
    end
    result
  end
end

quicksort.rb

module Quicksort
  module Simple
    def self.sort(array)
      return array if array.length <= 1
      less = []
      greater = []
      pivot = array.shift
      array.each do |elem|
        if elem <= pivot
          less << elem
        else
          greater << elem
        end
      end
      sort(less) + [pivot] + sort(greater)
    end
  end
end