Leetcode-268 Missing Number

#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?

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int len=nums.size();
        int ret=;
        for(int i=;i<len+;i++)
        {
            ret^=i;
        }
        for(int i=;i<len;i++)
        {
            ret^=nums[i];
        }
        return ret;
    }
};