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?

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

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class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int totalSum = nums.size()*(1+nums.size())/2;
        int thiSum = accumulate(nums.begin(), nums.end(), 0);
        return totalSum-thiSum;
    }
};