题目地址：https://leetcode.com/problems/ugly-number/open in new window
Total Accepted: 22335 Total Submissions: 67449 Difficulty: Easy
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: 14 is not ugly since it includes another prime factor 7.
Note:
1、 1istypicallytreatedasanuglynumber.；
2、 Inputiswithinthe32-bitsignedintegerrange:[−231,231−1].；
题目大意
如果一个数的因子只有2,3,5，那么这个数是丑数。判断一个数是不是丑数。
解题方法
除去2,3,5因子
把这个数中的所有的2,3,5的因子全部除去，剩余的数为1，则说明全部为这几个因子构成。
python解法。
class Solution(object):
def isUgly(self, num):
"""
:type num: int
:rtype: bool
"""
if num <= 0: return False
while num % 2 == 0:
num /= 2
while num % 3 == 0:
num /= 3
while num % 5 == 0:
num /= 5
return num == 1
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Java解法：
public static boolean isUgly(int num) {
if (num == 1) {
return true;
}
while (num >= 2 && num % 2 == 0) {
num = num / 2;
}
while (num >= 3 && num % 3 == 0) {
num = num / 3;
}
while (num >= 5 && num % 5 == 0) {
num = num / 5;
}
return num == 1;
}
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另外有精简的答案如下。
public class Solution {
public boolean isUgly(int num) {
int[] divides ={2,3,5};
for(int i = 0; i < divides.length && num > 0; i++){
while(num % divides[i] == 0){
num /= divides[i];
}
}
return num == 1;
}
}
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