326. Power of Three(easy)

Easy

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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?

 

循环除法：

C++ ：

/* * @Autor: SourDumplings * @Date: 2019-09-10 20:21:54 * @Link: https://github.com/SourDumplings/ * @Email: changzheng300@foxmail.com * @Description: https://leetcode.com/problems/power-of-three/ */ class Solution { public: bool isPowerOfThree(int n) { while (n > 1 && n % 3 == 0) { n /= 3; } return n == 1; } };

换底公式法1：

Java：

/* * @Autor: SourDumplings * @Date: 2019-09-10 20:32:57 * @Link: https://github.com/SourDumplings/ * @Email: changzheng300@foxmail.com * @Description: https://leetcode.com/problems/power-of-three/ * * 设3^i = n，则i = log3(n) = log10(n) / log10(3) * 判断这样得到的3^i还是不是n，或者i是不是整数即可（用 % 1判断） */ class Solution { public boolean isPowerOfThree(int n) { return n != 0 && (Math.log10(n) / Math.log10(3)) % 1 == 0; } }

换底公式法2：

Java:

/* * @Autor: SourDumplings * @Date: 2019-09-10 20:32:57 * @Link: https://github.com/SourDumplings/ * @Email: changzheng300@foxmail.com * @Description: https://leetcode.com/problems/power-of-three/ * * 设3^i = n，则i = log3(n) = log10(n) / log10(3) * 判断这样得到的3^i还是不是n，或者i是不是整数即可（用 % 1判断） */ class Solution { public boolean isPowerOfThree(int n) { if (n == 0) return false; int i = (int) (Math.log10(n) / Math.log10(3)); return Math.pow(3, i) == n; } }