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 n = nums.size();

        int res = 0;
        for(int i = 0; i <= n; i++)
            res ^= i;
        for(auto num:nums)
            res ^= num;

        return res;
    }
};