leetcode-- Ugly Number

题目: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.

Note that 1 is typically treated as an ugly number.

题目解析：即num是n个随意2、3、5的积。

One：直接法-先判断负数和1.然后以num%2、3、5是否为0为条件进行num=num/2、3、5的循环。最后判断num是否为1.是返回true，否返回false。  1个循环

public class Solution {    public boolean isUgly(int num) {        if(num<=0)return false;        if(num==1)return true;        while(num%2==0||num%3==0||num%5==0){            if(num%2==0)num/=2;            if(num%3==0)num/=3;            if(num%5==0)num/=5;                    }        if(num==1)return true;        else return false;    }}

Two：3个循环

public class Solution {    public boolean isUgly(int num) {        if(num<=0) return false;        if(num==1) return true;    while(num%2==0) num=num>>1;    while(num%3==0) num=num/3;    while(num%5==0) num=num/5;        return num==1;    }}

Three: 递归的方法

public class Solution {    public boolean isUgly(int num) {        if(num<=0) return false;        if(num==1) return true;    while(num%2==0) return isUgly(num/2);    while(num%3==0) return isUgly(num/3);    while(num%5==0) return isUgly(num/5);        return false;    }}