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 };
原文：http://www.cnblogs.com/VickyWang/p/6032786.html