#encoding: utf-8
#author: xu jin, 4100213
#date: Oct 27, 2012
#MergeSort
#to sort an array by using MergeSort algorithm
#example output:
#The original array is：[4, 32, 84, 58, 49, 40, 75, 29, 82, 21, 70, 37, 70]
#The sorted array is: [4, 21, 29, 32, 37, 40, 49, 58, 70, 70, 75, 82, 84]

MAX = 100
arrayInt = Array.new
for index in (0..12)
 arrayInt[index] = rand(100) #produce 12 random number
end
puts "The original array is：" + arrayInt.to_s

def merge(arr, left, middle, right)
 arrL ,arrR = Array.new, Array.new
 arrL[0..(middle - left)], arrR[0..(right - middle - 1)] = arr[left..middle], arr[middle + 1.. right]
 arrL[arrL.size] ,arrR[arrR.size]= MAX, MAX
 for k in (left..right)
  arrL.first = arrR.first ? (arr[k] = arrL.shift) : (arr[k] = arrR.shift)
 end
end

def merge_sort(arr, left, right)
 if left  right then
  middle = (left + right)/2
  merge_sort(arr, left, middle)
  merge_sort(arr, middle + 1, right)
  merge(arr, left, middle, right)
 end
end

merge_sort(arrayInt, 0, arrayInt.length-1)
puts "The sorted array is: " + arrayInt.to_s