Mergesort in Ruby

mergesort.rb

=begin
  Merge sort in ruby

  Referrence
  https://en.wikipedia.org/wiki/Merge_sort

  Big O complexity
  Time complexity (Average, Best, Worest cases): O(n log(n))
  Space complexity: O(n)
=end

class MergeSort
  # sort the array in ascending order with merge sort
  #
  # @params array [Array<Fixnum>]
  # @returns [Array<Fixnum>] sorted array
  def self.sort(array)
    return array if array.size == 1

    size       = array.size
    half_index = (size / 2.0).floor
    left_ary   = sort(array[0...half_index])
    right_ary  = sort(array[half_index...size])

    merge_sorted_arrays(left_ary, right_ary)
  end

  private

  # Merge 2 sorted arrays, Time: O(n), Space: O(n)
  #
  # @params ary1 [Array<Fixnum>] sorted array 1
  # @params ary2 [Array<Fixnum>] sorted array 2
  # @returns [Array<Fixnum>] sotred array that merged array 1 and array 2
  def self.merge_sorted_arrays(ary1, ary2)
    ary = []
    index1 = 0
    index2 = 0

    while(index1 < ary1.size || index2 < ary2.size)
      if index1 == ary1.size
        ary += ary2[index2...ary2.size]
        index2 = ary2.size
        break
      end

      if index2 == ary2.size
        ary += ary1[index1...ary1.size]
        index1 = ary1.size
        break
      end

      if ary1[index1] < ary2[index2]
        ary << ary1[index1]
        index1 += 1
      elsif ary1[index1] > ary2[index2]
        ary << ary2[index2]
        index2 += 1
      else
        ary << ary1[index1]
        ary << ary2[index2]
        index1 += 1
        index2 += 1
      end
    end

    return ary
  end
end

ary = [6, 5, 3, 1, 8, 7, 2, 4]
print MergeSort.sort(ary)
puts