263. Ugly Number.cpp

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

Solution is pretty straightforward, keep dividing and judge
*/
class Solution {
public:
    bool isUgly(int num) {
        if ( num % 2 != 0 && num % 3 != 0 && num % 5 != 0 && num != 1 || 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 ? true : false;
    }
};

//Optimized
class Solution {
public:
    bool 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;
    }
};