[LeetCode] Missing Number

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

For example,
Given nums = [0, 1, 3] return 2.

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

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int size = nums.size();
        int total = 0;
        for(int i=0; i<size; i++)
        {
            total += nums[i];
        }
        return size*(size+1)/2 - total;
    }
};