def mergeSort( A ):
    if len(A)==1: #Base Case
        return
    else:
        middle = len(A)//2  #You could also do int(len(A)/2)

        #Create two temporary lists with COPIES of the two halves
        left = A[:middle]   
        right = A[middle:] 
  
        mergeSort(left) 
        mergeSort(right)

        #Set up indices for where we are in each lists
        frontLeft = 0
        frontRight = 0
        frontMain = 0

        # Copy data from L and R back in to A 
        while frontLeft < len(left) and frontRight < len(right): 
            if left[frontLeft] < right[frontRight]: 
                A[frontMain] = left[frontLeft] 
                frontLeft = frontLeft +1
            else: 
                A[frontMain] = right[frontRight] 
                frontRight = frontRight +1
            frontMain = frontMain + 1
          
        # Checking which pile still has elements left 
        while frontLeft < len(left): 
            A[frontMain] = left[frontLeft] 
            frontLeft += 1
            frontMain += 1
          
        while frontRight < len(right): 
            A[frontMain] = right[frontRight] 
            frontRight += 1
            frontMain += 1

    

data = list(range(100)) 
import random
random.shuffle(data)


print(data)
mergeSort(data)
print(data)