263. Ugly number

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.

Design: if a number not ugly, and it can be divided by 2/3/5. then the result still is a not ugly number.

class Solution {
public:
    bool isUgly(int num) {
        if(num < 1) return false;
        if(num < 7) 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;
    }
};