难度: Easy
原题连接
内容描述
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 is typically treated as an ugly number.
Input is within the 32-bit signed integer range: [−231, 231 − 1].
思路 1 - 时间复杂度: O(1)- 空间复杂度: O(1)******
因为其prime factors 只包括 2, 3, 5，所以比如如果能被 2 整除， n = n / 2， 直到不能被2整除，然后同样对3,5检验，如果最终结果为1，那么就是ugly number，否则不过关
注意一下边界条件，当num为0的时候，return一下False
class Solution(object):
def isUgly(self, num):
"""
:type num: int
:rtype: bool
"""
if num <= 0:
return False
if num <= 3:
return True
while num % 2 == 0:
num = num / 2
while num % 3 == 0:
num = num / 3
while num % 5 == 0:
num = num / 5
return True if num == 1 else False