leetcode, LC14: single-number-ii

1 题目描述

题目描述
如今有一个整数类型的数组，数组中只有一个元素只出现一次，其他元素都出现三次。你须要找出只出现一次的元素
注意：
你须要给出一个线性时间复杂度的算法，你能在不使用额外内存空间的状况下解决这个问题么？

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?

2 解题思路

超出个人知识范畴了。。

3 代码实现

class Solution {
public:
    /** * * @param A int整型一维数组 * @param n int A数组长度 * @return int整型 */
    int singleNumber(int* A, int n) {
        // write code here
        int ones = 0;
        int twos = 0;
        int threes;
        for(int i = 0; i < n; i++){
            int elem = A[i];
            twos |= ones & elem;
            ones ^= elem;
            threes = ones & twos;
            ones &= ~threes;
            twos &= ~threes;
        }
        return ones;
    }
};

4 运行结果

运行时间：3ms
占用内存：484k