Ugly Number 517

Question

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.

Notice

Note that 1 is typically treated as an ugly number.

Example

Given num = 8 return true

Given num = 14 return false

Solution

判断能否被2，3，5除尽。

代码如下：

public class Solution {
    /**
     * @param num an integer
     * @return true if num is an ugly number or false
     */
    public boolean isUgly(int num) {
        // Write your code here
        if(num <= 0){
            return false;
        }

        if(num == 1){
            return true;
        }

        while(num >= 2 && num % 2 == 0){
            num /= 2;
        }

        while(num >= 3 && num % 3 == 0){
            num /= 3;
        }

        while(num >= 5 && num % 5 == 0){
            num /= 5;
        }

        return num == 1;
    }
}