leetcode——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 n = nums.size();
        if(n==0)
            return -1;
         int res=nums[0] ;  
        for(int i=1;i<n;i++)
        {
            res = res^nums[i];
        }
        return res;
    }
};