326. Power of Three*

326. Power of Three*

https://leetcode.com/problems/power-of-three/

题目描述

Given an integer, write a function to determine if it is a power of three.

Example 1:

Input: 27
Output: true

Example 2:

Input: 0
Output: false

Example 3:

Input: 9
Output: true

Example 4:

Input: 45
Output: false

Follow up:
Could you do it without using any loop / recursion?

C++ 实现 1

使用递归做.

class Solution {
public:
    bool isPowerOfThree(int n) {
        if (n == 1) return true;
        if (n % 3 != 0 || n == 0) return false;
        n /= 3;
        return isPowerOfThree(n);
    }
};

C++ 实现 2

使用循环做. 来自 LeetCode Submission.

class Solution {
public:
    bool isPowerOfThree(int n) {
        while (n && n%3 == 0) {
            n /= 3;
        }
        return n == 1;
    }
};

C++ 实现 3

数学方法.

class Solution {
public:
    bool isPowerOfThree(int n) {
 		return fmod(log10(n)/log10(3), 1)==0;        
    }
};