263. Ugly Number

• Difficulty: Easy

• Topics: Math

• Similar Questions:

  • Happy Number

  • Count Primes

  • Ugly Number II

Problem:

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].

Solutions:

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;
    }
};