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. }