Single Number

描述

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?

异或，不仅能处理两次的情况，只要出现偶数次，都可以清零。

class Solution {
public:
int singleNumber(vector<int>& nums) {
int x = 0;
for (size_t i = 0; i < nums.size(); ++i)
x ^= nums[i];
return x;

}
};