Ugly Number

描述

Write a function 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.

分析

思路很简单，把n里面的2,3,5 全部消掉，看最后能不能剩下1。

代码

  1. // Ugly Number
  2. // Time complexity: O(logn), Space complexity: O(1)
  3. public class Solution {
  4.     public boolean isUgly(int num) {
  5.         if (num == 0) return false;
  6.         while (num % 2 == 0) num /= 2;
  7.         while (num % 3 == 0) num /= 3;
  8.         while (num % 5 == 0) num /= 5;
  9.         return num == 1;
  10.     }
  11. }

相关题目

原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/java/number-theory/ugly-number.html