LeetCode 263 Ugly Number

Problem:

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.

Summary:

判断一个数是不是ugly number，即质因子只有2、3、5的数。

Analysis:

判断方法即为不断除以2、3、5，看最终能否得到1。以下两种方法大同小异。

 1 class Solution {
 2 public:
 3     bool isUgly(int num) {
 4         if (num <= 0) return false;
 5         
 6         while (num != 1) {
 7             if (num % 2 == 0) num /=2;
 8             else if (num % 3 == 0) num /=3;
 9             else if (num % 5 == 0) num /= 5;
10             else return false;
11         }
12         
13         return true;
14     }
15 };

 1 class Solution {
 2 public:
 3     bool isUgly(int num) {
 4         if (num <= 0) return false;
 5         
 6         while (num >= 2 && num % 2 == 0) num /= 2;
 7         while (num >= 3 && num % 3 == 0) num /= 3;
 8         while (num >= 5 && num % 5 == 0) num /= 5;
 9         
10         return num == 1;
11     }
12 };