Method to count the number of inversion in an array of numbers

inversion.rb

def count_inversion arr

  def count_and_merge arr1, arr2
    arr = []
    j = 0
    i = 0
    count = 0
    while (i != arr1.size) && (j != arr2.size)

      if arr1[i] < arr2[j]
        arr << arr1[i]
        i = i+1
      elsif arr1[i] == arr2[j]
        while arr1[i] == arr2[j]
          arr << arr1[i]
          i = i+1
        end
        arr << arr2[j]
        j = j+1
        count = count + arr1.size - i
      else
        arr << arr2[j]
        j = j+1
        count = count + arr1.size - i 
      end
    end

    if i == arr1.size 
      arr2[j..-1].each { |m| arr << m }
    end
    
    if j == arr2.size
      arr1[i..-1].each { |m| arr << m }
    end
    
    return arr,count 
    
  end


  if arr.size > 2
    arr1,count1 = count_inversion arr[0..arr.size/2]
    arr2,count2 = count_inversion arr[arr.size/2+1..-1]
    arr3,count3 = count_and_merge(arr1,arr2)

    return arr3,count1+count2+count3
  else
    count = 0
    return arr,0 if arr.size == 1 
    if arr[0] > arr[1]
      arr[0], arr[1] = arr[1], arr[0]
      count = 1
    end
    return arr,count 
  end

end

inversion_iter.rb

def count_inversion arr

  temp_array = Array(arr.size)
  inv_count = 0
  blksize = 1
  
  while true do 
    blksize = 2*blksize
    (0..arr.size-1).step(blksize) do |m|
      #merge two partial blks
      blk1start = m
      blk1count = blksize/2 if arr.size >= blk1start + blksize/2
      blk1count = arr.size - blk1start if arr.size < blk1start + blksize/2
      blk1end = blk1start + blk1count - 1
      blk2start = blk1start + blk1count 
      blk2count = blksize/2 if arr.size >= blk2start + blksize/2
      blk2count = arr.size - blk2start if arr.size < blk2start + blksize/2
      blk2end = blk2start + blk2count - 1

      # copy first half into new temp array if required
      if blk2count != 0 
        next if arr[blk1end] < arr[blk2start]
        j = 0
        (blk1start..blk1end).each { |m| temp_array[j] = arr[m]; j += 1 }
      end

      next if blk2count == 0 
      # compare and save 
      tempcount = j
      j = 0
      k = 0
      index = blk1start
      while (j < tempcount) and  (k < blk2count)
        if (temp_array[j] <= arr[blk2start + k])
          arr[index] = temp_array[j]
          j += 1
          index += 1
        elsif (temp_array[j] > arr[blk2start + k])
          arr[index] = arr[blk2start + k]
          k += 1
          index += 1
          inv_count += (tempcount - j)
        end 

      end

      # if (j == tempcount)
      #   while (k != blk2count)
      #     arr[index] = arr[blk2start + k]
      #     k += 1
      #     index += 1
      #   end
      # end
      if (k == blk2count)
        while (j != tempcount)
          arr[index] = temp_array[j]
          j += 1
          index += 1 
        end 
      end
    end
    break if blksize > arr.size
  end
  return arr,inv_count
end