mergesort() python code example

Example 1: Merge Sort python

def merge_sort(arr):
    # The last array split
    if len(arr) <= 1:
        return arr
    mid = len(arr) // 2
    # Perform merge_sort recursively on both halves
    left, right = merge_sort(arr[:mid]), merge_sort(arr[mid:])

    # Merge each side together
    return merge(left, right, arr.copy())


def merge(left, right, merged):

    left_cursor, right_cursor = 0, 0
    while left_cursor < len(left) and right_cursor < len(right):
      
        # Sort each one and place into the result
        if left[left_cursor] <= right[right_cursor]:
            merged[left_cursor+right_cursor]=left[left_cursor]
            left_cursor += 1
        else:
            merged[left_cursor + right_cursor] = right[right_cursor]
            right_cursor += 1
            
    for left_cursor in range(left_cursor, len(left)):
        merged[left_cursor + right_cursor] = left[left_cursor]
        
    for right_cursor in range(right_cursor, len(right)):
        merged[left_cursor + right_cursor] = right[right_cursor]

    return merged

Example 2: merge sort in python

def mergesort(list1):
    if len(list1) >1 :
    
        mid = len(list1)//2
        left_list = list1[:mid]
        right_list = list1[mid:]
        mergesort(left_list) #Using recursion down here for the sub list
        mergesort(right_list) #Using recursion down here for the sub list
        i = 0
        j = 0
        k = 0
        while i<len(left_list) and j<len(right_list):
            if left_list[i]< right_list[j]:
                list1[k] = left_list[i]
                i+=1
                k+=1
            else:
                list1[k] = right_list[j]
                j+=1
                k+=1
        while i < len(left_list): # I did this as for the end condition of above loop as when i or j will be equal to len(left/right list)  
            list1[k] = left_list[i]
            i+=1
            k+=1

        while j < len(right_list):
            list1[k] = right_list[j]
            j+=1
            k+=1
#Start watching from here and then as when function call will come then go check function
n = int(input("Enter how many element you want in the list : "))
list1 = [int(input()) for i in range(n)]
mergesort(list1)
print("sorted list : " + str(list1))