Missing Number Python

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

Example 1:

Input: [3,0,1]
Output: 2

Example 2:

Input: [9,6,4,2,3,5,7,0,1]
Output: 8

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity ?

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        n = len(nums)
        total_sum = int((n*(n+1))/2)
        for i in nums:
            total_sum-=i
        return total_sum


Time Complexity : O(n)
Space Complexity : O(1)

Note : Here array starts with 0 not 1 so n = len(nums) 

if it starts with 1 like natural numbers then n = len(nums)+1