lintcode:Ugly Number I

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.

注意事项

Note that 1 is typically treated as an ugly number.

样例

Given num = 8 return true
Given num = 14 return false

解题

直接递归

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;
        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;

    }
}

while 循环‘

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;
        while(num %2 ==0)
            num/=2;
        while(num %3 ==0)
            num/=3;
        while(num%5 ==0)
            num/=5;

        return num==1;

    }
}