merge_sort.py

def merge(arr, l, m, r):
    n1 = m - l + 1
    n2 = r - m
 
    L = [0] * (n1)
    R = [0] * (n2)
 
    for i in range(0, n1):
        L[i] = arr[l + i]
 
    for j in range(0, n2):
        R[j] = arr[m + 1 + j]
 
    # Merge the temp arrays back into arr[l..r]
    i = 0    
    j = 0   
    k = l   
 
    while i < n1 and j < n2:
        if L[i] <= R[j]:
            arr[k] = L[i]
            i += 1
        else:
            arr[k] = R[j]
            j += 1
        k += 1
 
    # Let's Copy the remaining elements of L[], if there is any
    while i < n1:
        arr[k] = L[i]
        i += 1
        k += 1
 
    # Let's Copy the remaining elements of R[], if there is any
    while j < n2:
        arr[k] = R[j]
        j += 1
        k += 1
 
# l is for left index and r is right index of the
# sub-array of arr to be sorted
 
def mergeSort(arr, l, r):
    if l < r:
        m = l+(r-l)//2
        # Sort first and second halves
        mergeSort(arr, l, m)
        mergeSort(arr, m+1, r)
        merge(arr, l, m, r)
 

arr = [25,15,9000,122,9099]
n = len(arr)
print("Given array is")
for i in range(n):
    print("%d" % arr[i],end=" ")
 
mergeSort(arr, 0, n-1)
print("\n\nSorted array is")
for i in range(n):
    print("%d" % arr[i],end=" ")