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