136. Single Number

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