326.是否为3的平方根 IsPowerOfThree

public static bool IsPowerOfThree(int n) {
	if (n == 1) {
		return true;
	}
	double num = n;
	bool isPower = false;
	while (num >= 1) {
		num = num / 3;
		if (num == 1 && num == (int)num) {
			return true;
		}
	}
	return isPower;
}

public static bool IsPowerOfThree(int n) {
	if (n == 1) {
		return true;
	} else if (n == 0 || n % 3 > 0) {
		return false;
	} else {
		return IsPowerOfThree(n / 3);
	}
}

class Solution {
public:
    bool isPowerOfThree(int n) {
        return (n > 0 && int(log10(n) / log10(3)) - log10(n) / log10(3) == 0);
    }
};