Ugly Number

Q:

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.

Example 1:

Input: 6
Output: true
Explanation: 6 = 2 × 3

Example 2:

Input: 8
Output: true
Explanation: 8 = 2 × 2 × 2

Example 3:

Input: 14
Output: false 
Explanation: 14 is not ugly since it includes another prime factor 7.

Note:

1. 1 is typically treated as an ugly number.
2. Input is within the 32-bit signed integer range: [−231,  231 − 1].

A:

递归检查即可

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

Mistakes:
 没有考虑0的情况，导致死循环