Ugly Number

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.

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. 1 is typically treated as an ugly number.
2. Input is within the 32-bit signed integer range: [−2³¹,  2³¹ − 1].

Solution(javascript)

const isUgly = (num) => {
  const memo = []
  const aux = (n) => {
    if (memo[n] !== undefined) {
      return memo[n]
    }
    if (n === 1 || n === 2 || n === 3 || n === 5 || n === 4) {
      return true
    }
    if (n < 5) {
      return false
    }
    memo[n] = aux(n / 2) || aux(n / 3) || aux(n / 5)
    return memo[n]
  }
  return aux(num)
}