leetcode---Single Number---异或

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 n = nums.size();        if(n == 0)            return 0;        int ans = 0;        for(int i=0; i<n; i++)            ans ^= nums[i];        return ans;    }};