Given an array of integers, every element appears twice except for one. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

class Solution {public:    int singleNumber(vector
     
      & nums) {        int ans = 0;        vector
      
       ::const_iterator it = nums.cbegin();        for (; it != nums.cend(); ++it) {            ans^=*it;        }        return ans;    }};