263. Ugly Number

问题：
Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.

Note that 1 is typically treated as an ugly number.

我的解答：

class Solution {
public:
    bool isUgly(int num) {
     if (num == 1) return true;
        if (num <= 0) return false;
        while (num % 2 == 0) num /= 2;
        while (num % 3 == 0) num /= 3;
        while (num % 5 == 0) num /= 5;
        return num == 1;
    }
};

解释：
把2,3,5的因数都去掉。看看最后还有什么。