268. Missing Number（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 len=nums.size();
       int sum1=0;
       int sum2=0;
       for(int i=0;i<len;i++)
       {
           sum1+=nums[i];
       }
       for(int i=0;i<=len;i++)
       {
           sum2+=i;
       }
      return sum2-sum1;
    }
};