*Ugly number

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題目：

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.

題目大意：

編寫程式判斷一個給定的數字是否為“醜陋數” ugly number

醜陋數是指只包含質因子2, 3, 5的正整數。例如，6, 8是醜陋數而14不是，因為它包含額外的質因子7

注意，數字1也被視為醜陋數

解題思路：

將輸入數重複除2, 3, 5，判斷得數是否為1即可

時間複雜度：

記num = 2^a * 3^b * 5^c * t，程式執行次數為 a + b + c，換言之，最壞情況為O(log num)

 

 1 public class Solution { 2     public boolean isUgly(int num)  3     { 4         if(num <= 0) return false; 5         int [] prime = {2,3,5}; 6         for (int x:prime) 7         { 8             while(num%x==0) 9             num/=x;10         }11         12         return num==1;13         14     }15 }

reference: http://bookshadow.com/weblog/2015/08/19/leetcode-ugly-number/

*Ugly number