137. Single Number II

目录

• 题目描述
• 思路
• 代码实现

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?

思路

利用位运算，分别求出这个只出现一次的数各个二进制位上的值

代码实现

class Solution {
public:
    int singleNumber(int A[], int n) {

    	int result = 0;
        //分别求出结果各个位的值
        //故先来一个循环遍历结果的每一位
    	for(int i =0;i < sizeof(int)*8;i++)
    	{                                  

    		int mask = 1<<i;
    		int bitCnt = 0;
    		for(int j = 0;j < n;j++)
    		{
    			if((A[j] & mask)!=0)
    				bitCnt++;

    		}

    		result|= (bitCnt%3)<<i;

    	}

    	return result;
        
    }
};