268. Missing Number

题目来源【Leetcode】

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 s = nums.size();        int sum = 0;        for(int i = 0; i <= s; i++){            sum += i;           }        for(int i = 0; i < s; i++ ){            sum -= nums[i];        }        return sum;    }};