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?

AC代码如下（思想：等差数列的和）：

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