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.

Solution:

Recursive,

Base case: num==1 which is ugly number.

If num can be divided by 2, 3 ,5 recursively check num/2 or num/3 or num/5. 

 public boolean 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;  
   }  

Iterative: same idea:

 public boolean isUgly(int num) {  
     if(num<=0) return false;  
     while(num%2==0) num/=2;   
     while(num%3==0) num/=3;   
     while(num%5==0) num/=5;  
     return num==1;  
   }