263. Ugly Number (Python)

Related Topic

Math.

Description

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.

Sample I/O

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].

Methodology

Iterate each prime factors, use n to mod each factor until the remainder is no more 0. Then move to next factor. The result will be 1 if the number is ugly.

def isUgly(self, num: int) -> bool:
        if num==0: return False
        for f in [2,3,5]:
            while num%f==0:
                num/=f
            if num == 1:
                return True

BigO

Time complexity : O(n) where n is sqrt(number).