326. Power of Three

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

Problem

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?

Solution

1. Recursive

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

2. Base Conversion

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

3. Logarithm

class Solution {
public:
    bool isPowerOfThree(int n){
        if (n <= 0) return false;
        double result = log10(n) / log10(3); 
        return (result - floor(result)) == 0;
    }
};

• #math

• #important