LeetCode 136 Single Number 数组中除一个数外其他数都出现两次，找出只出现一次的数

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

 class Solution {
 public:
     int singleNumber(vector<int>& nums) {
         int size=nums.size();
         if(size==||nums.empty())
             return ;
         int res=;
         for(int i=;i<size;++i)
             res^=nums[i];
         return res;
     }
 };