Leetcode-Single Number II

http://oj.leetcode.com/problems/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;    
                }
            };