leetcode Power of Three

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

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

本文是leetcode 326 Power of Three 题解，

更多本博客题解见 http://www.hrwhisper.me/leetcode-algorithm-solution/

方法一：

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

方法二：

C++

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

方法三：

class Solution {
public:
	bool isPowerOfThree(int n) {
		return n <= 0 ? false : n == pow(3, round(log(n) / log(3)));
	}
};

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