# Leetcode-Single Number II

## 题目描述

Given an array of integers, every element appears three times 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.
int once = 0;//记录%3余1的bit
int twice = 0;//记录%3余2的bit
for(int i = 0; i < n; i++)
{
twice |= once & A[i]; //或运算
once ^= A[i];
int not_three = ~(once & twice);
once = not_three & once;
twice = not_three & twice;
}
return once;
}
};
```