题目：

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?

代码：

1 class Solution {
2 public:
3     int singleNumber(vector<int>& nums) {
4         int result = 0;
5         for (auto c : nums)
6             result ^= c;
7         return result;
8     }
9 };