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;
}
};