LeetCode - 136. Single Number

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?

思路与步骤：

极低效率思路：

用 HashMap

先排序

高效思路：

学习别人的思路

用XOR，注意数组中用到抑或时常常会所有的数字一起抑或，因为在数组中单独两个数字抑或意义不大。

编程实现：

这里只给出用抑或实现的程序

public class Solution {
    public int singleNumber(int[] nums) {
        int result = 0;
        for (int n: nums)   result ^= n;
        return result;
    }
}