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].
这道题让我们检测一个数是否为丑陋数，所谓丑陋数就是其质数因子只能是 2，3，5。那么最直接的办法就是不停的除以这些质数，如果剩余的数字是1的话就是丑陋数了，参见代码如下：
解法一：
class Solution {
public:
bool isUgly(int num) {
while (num >= ) {
if (num % == ) num /= ;
else if (num % == ) num /= ;
else if (num % == ) num /= ;
else return false;
}
return num == ;
}
};
我们也可以换一种写法，分别不停的除以 2，3，5，并且看最后剩下来的数字是否为1即可，参见代码如下：
解法二：
class Solution {
public:
bool isUgly(int num) {
if (num <= ) return false;
while (num % == ) num /= ;
while (num % == ) num /= ;
while (num % == ) num /= ;
return num == ;
}
};
Github 同步地址：
https://github.com/grandyang/leetcode/issues/263
类似题目：
参考资料：
https://leetcode.com/problems/ugly-number/
https://leetcode.com/problems/ugly-number/discuss/69225/My-2ms-java-solution
https://leetcode.com/problems/ugly-number/discuss/69214/2-4-lines-every-language
https://leetcode.com/problems/ugly-number/discuss/69332/Simple-java-solution-with-explanation
https://leetcode.com/problems/ugly-number/discuss/69308/Java-solution-greatest-divide-by-2-3-5