Ugly Number

https://leetcode.com/problems/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. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.

Note that 1 is typically treated as an ugly number

Thoughts

检查是否能一直整除2, 3或5下去.

Code

class Solution {
    public boolean isUgly(int num) {
        int[] ps = new int[]{2, 3, 5};
        while (num > 1) {
            boolean found = false;
            for (Integer p : ps) {
                if (num % p == 0) {
                    num = num / p;
                    found = true;
                    break;
                }
            }

            if (!found) {
                return false;  
            }
        }

        return num == 1;
    }
}

Analysis

时间复杂度O(lgN)