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Ugly Number

Problem​

An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.

Given an integer n, return true if n is an ugly number.

 

Example 1:

Input: n = 6
Output: true
Explanation: 6 = 2 × 3

Example 2:

Input: n = 1
Output: true
Explanation: 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5.

Example 3:

Input: n = 14
Output: false
Explanation: 14 is not ugly since it includes the prime factor 7.

 

Constraints:

  • -231 <= n <= 231 - 1

Solution​

/**
 * @param {number} num
 * @return {boolean}
 */
var isUgly = function(num) {
    if (num <= 0) {
        return false;
    }
    while (!(num % 2)) num /= 2;
    while (!(num % 3)) num /= 3;
    while (!(num % 5)) num /= 5;
    return num === 1;
};

Keep dividing n by 2, 3 and 5 until there is a non-zero remainder.