Ugly Number问题及解法

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问题描述：

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.

问题分析：

只要一个正整数中的素因子不止2,3,5其中的几个，那么就不是ugly number，所以，我们只需要把该整数所有的2,3,5素因子除完，看看最后值是否等于1即可。

过程详见代码：

复制代码

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class Solution {
public:
    bool isUgly(int num) {
        int last = num;
    	while(num > 0)
    	{
    		if(num % 2 == 0) num = num / 2;
        	if(num % 3 == 0) num = num / 3;
        	if(num % 5 == 0) num = num / 5;
        	if(last == num) break;
        	last = num;
		}
		return num == 1; 
    }
};