Java程序練習-Ugly Numbers

描述
Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, ...
shows the first 10 ugly numbers. By convention, 1 is included.
Given the integer n,write a program to find and print the n'th ugly number.

輸入
Each line of the input contains a postisive integer n (n <= 1500).Input is terminated by a line with n=0.
輸出
For each line, output the n’th ugly number .:Don’t deal with the line with n=0.
樣例輸入
1
2
9
0
樣例輸出
1
2
10
參考代碼

1. import java.io.BufferedReader;  
2. import java.io.IOException;  
3. import java.io.InputStreamReader;  
4. import java.util.Iterator;  
5. import java.util.Set;  
6. import java.util.TreeSet;  
7. public class Main {  
8.     public static int N = 1601;  
9.     public static Set<Integer> set = new TreeSet<Integer>();  
10.     public static void main(String[] args) throws Exception, IOException{  
11.         init();  
12.         BufferedReader  cin = new BufferedReader (new InputStreamReader(System.in));  
13.         while(true){  
14.             int n = Integer.parseInt(cin.readLine());  
15.             if(0 == n)  
16.                 break;  
17.             System.out.println(setAt(n));  
18.         }  
19.     }  
20.     private static void init() {  
21.         set.add(1);  
22.         int n = 1;  
23.         int loop = 1;  
24.         while(set.size() < N){  
25.             add2set(n);  
26.             n = setAt(++ loop);  
27.         }  
28.     }  
29.     private static int setAt(int p) {  
30.         int n = 0;  
31.         Iterator<Integer> it = set.iterator();  
32.         int j = 1;  
33.         while(it.hasNext()){  
34.             n = it.next();  
35.             if(j == p)  
36.                 return n;  
37.             j ++;  
38.         }  
39.         return n;  
40.     }  
41.     private static void add2set(int n) {  
42.         set.add(n * 2);  
43.         set.add(n * 3);  
44.         set.add(n * 5);  
45.     }  
46. }