- 题目描述
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.
Example 1:
Input: 6
Output: true
Explanation: 6 = 2 × 3
Example 2:
Input: 8
Output: true
Explanation: 8 = 2 × 2 × 2
Example 3:
Input: 14
Output: false
Explanation:14is not ugly since it includes another prime factor7.
Note:
-
1is typically treated as an ugly number. - Input is within the 32-bit signed integer range: [−231, 231 − 1].
- 解题思路
虽然这道题属于简单类型，但是我小学数学不太好，质因数的概念并不是特别清楚，查了下百度百科才有了思路。
所以，也在这儿记录下。另外，自己实现的算法也不是特别好，也正好把自己的和讨论区的实现对比下～
- 我的代码
class Solution {
public:
bool isUgly(int num) {
if(num <= )
return false;
while(num != )
{
if(num % == )
{
num = num / ;
}
else if(num % == )
{
num = num / ;
}
else if(num % == )
{
num = num / ;
}
// other prime factor
else
{
return false;
}
}
return true;
}
};
- 更快的代码
// 这个代码，减少了判断，性能就高了～确实也没必要判断。
// 对问题理解不深刻，无法认识应用隐含条件。
class Solution {
public:
bool isUgly(int num) {
if(num == ) return false;
while(num % == ) num /= ;
while(num % == ) num /= ;
while(num % == ) num /= ;
if(num > ) return false;
if(num == ) return true;
return false;
}
};