263. 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.

第一回写的solution，想得太多，代码冗杂，运行时间也偏长：

public class Solution {    public boolean isUgly(int num) {        if(num==1){            return true;        }        if(num==0){            return false;        }        while((num&1)==0){            num/=2;        }        if(num==1){            return true;        }        String sum_bit=Integer.toString(num);        int sum=0;        for(int i=0;i<sum_bit.length();++i){            sum=sum+sum_bit.charAt(i)-48;            }        while((sum%3)==0){            num/=3;            sum_bit=Integer.toString(num);            sum=0;            for(int i=0;i<sum_bit.length();++i){                sum=sum+sum_bit.charAt(i)-48;            }                    }        if(num==1){            return true;        }        sum_bit=Integer.toString(num);        char c=sum_bit.charAt(sum_bit.length()-1);        while(c=='5'){            num/=5;            sum_bit=Integer.toString(num);            c=sum_bit.charAt(sum_bit.length()-1);            }        if(num==1){            return true;        }         else{            return false;        }            }}

再一回，想简单点：

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

在Discuss中看到的更简洁的Solution：

public class Solution {    public boolean isUgly(int num) {        for(int i=2;i<6&&num>0;++i)            while(num%i==0)                num/=i;        return num==1;                    }}