leetcode 342. Power of Four 4的幂指数-蒲公英云

leetcode 342. Power of Four 4的幂指数

野性酷女 2022-06-07 01:15 309阅读 0赞

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:
Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?

最直接的方法就是使用log函数去做判断，后来网上发现一个使用位计算的方法，直接看代码吧！

建议和这一道题leetcode 326. Power of Three 3的幂指数一起学习。

代码如下：

public class Solution 
{
    public boolean isPowerOfFourByLog(int num) 
    {
        double res=Math.log10(num) / Math.log10(4);
        return (res-(int)(res))==0?true:false;    
    }
    public boolean isPowerOfFour(int num) 
    {
        if(num<=0)
            return false;
        return (num&(num-1))==0 && (num&0x55555555)==num;
    }
}

下面是C++的做法

代码如下：

#include <iostream>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <queue>
#include <stack>
#include <string>
#include <climits>
#include <algorithm>
#include <sstream>
#include <functional>
#include <bitset>
#include <numeric>
#include <cmath>
#include <regex>
using namespace std;
class Solution 
{
public:
    bool isPowerOfFour(int num)
    {
        double res = log10((double)num) / log10(4);
        return (res - (int)res) == 0 ? true : false;
    }
};