leetcode 268. 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?

呵呵

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