题目描述：

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?

解题方案：

该题利用异或可以方便求解，下面本题是代码：

 1 class Solution { 2 public: 3     int singleNumber(int A[], int n) { 4         int result = A[0]; 5         for(int i = 1; i < n; ++i){ 6             //利用异或 7             result = result ^ A[i]; 8         } 9         return result;10     }11 };

Single Number