[leetcode]53 Ugly Number

题目链接：https://leetcode.com/problems/ugly-number/

Runtime：8ms

1、问题

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.

2、分析

很显然，num<=0 的所有情况都应该返回false，因为因子中有负数，不单单包含2， 3， 5。其次做因子判断，如果数字不能被2、3、5整除，那么返回false，否则返回true啦。

3、小结

没有进行分析就直接写代码是不对滴：

1、没考虑负数

2、while条件不正确：1 < num

3、精简代码：不用对1单独判断

4、实现

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

5、反思

思考后下笔，良策！