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.

Analyse: Continuously divide the number by 2, 3, 5. If the remaining number is one, then it's a ugly number.

Runtime: 4ms.

 1 class Solution {
 2 public:
 3     bool isUgly(int num) {
 4         if(num == 0) return false;
 5         if(num == 1) return true;
 6         
 7         while(num % 2 == 0) num /= 2;
 8         while(num % 3 == 0) num /= 3;
 9         while(num % 5 == 0) num /= 5;
10         
11         if(num == 1) return true;
12         return false;
13     }
14 };

Runtime: 8ms.

 1 class Solution {
 2 public:
 3     bool isUgly(int num) {
 4         if(num == 0) return false;
 5         if(num == 1) return true;
 6         
 7         int arr[] = {2, 3, 5};
 8         int index = 0;
 9         while(index < 3){
10             while(num % arr[index] == 0) num /= arr[index];
11             index++;
12         }
13         
14         if(num == 1) return true;
15         return false;
16     }
17 };