Try to remove the prime factors of 2, 3, and 5 as many as possible and see if the remaining number is 1

```
class Solution {
public:
bool isUgly(int num) {
if(num<=0) return false;
int factor[] ={2,3,5}, i=0;
for(i=0; i<3;++i)
while(num%factor[i] == 0) num/=factor[i];
return num==1;
}
};
```