【LeetCode】263. Ugly Number

题目：

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.

可以用循环，也可以用递归。

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);
        if (num % 3 == 0)
                return isUgly(num/3);
        if (num % 5 == 0)
                return isUgly(num/5);
 
        return false;
    }
};