# Merge Sort | Time Complexity O(NlogN)
def mergeSort(alist):
    print("Splitting ", alist)
    if len(alist) > 1:
        mid = len(alist) // 2
        lefthalf = alist[:mid]
        righthalf = alist[mid:]

        mergeSort(lefthalf)
        print("LeftHalf ", lefthalf)
        mergeSort(righthalf)
        print("RightHalf ", righthalf)


        i = 0
        j = 0
        k = 0

        while i < len(lefthalf) and j < len(righthalf):
            if lefthalf[i] < righthalf[j]:
                alist[k] = lefthalf[i]
                i = i+1
            else:
                alist[k] = righthalf[j]
                j = j+1
            k = k+1

        while i < len(lefthalf):
            alist[k] = lefthalf[i]
            i = i+1
            k = k+1

        while j < len(righthalf):
            alist[k] = righthalf[j]
            j = j+1
            k = k+1
    print("Merging ", alist)


alist = [54, 26, 93, 17, 31, 44, 55, 20]
mergeSort(alist)
print(alist)