## 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?

## 代码

```
class Solution {
public:
int singleNumber(int A[], int n) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
if(A == NULL || n == 0)
return 0;
int result = A[0];
for(int i = 1; i < n; i++)
result = result ^ A[i];
return result;
}
};
```