Java程序练习-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.

输入
Each line of the input contains a postisive integer n (n <= 1500).Input is terminated by a line with n=0.
输出
For each line, output the n’th ugly number .:Don’t deal with the line with n=0.
样例输入
1
2
9
0
样例输出
1
2
10
参考代码

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.Iterator; import java.util.Set; import java.util.TreeSet; public class Main { public static int N = 1601; public static Set<Integer> set = new TreeSet<Integer>(); public static void main(String[] args) throws Exception, IOException{ init(); BufferedReader cin = new BufferedReader (new InputStreamReader(System.in)); while(true){ int n = Integer.parseInt(cin.readLine()); if(0 == n) break; System.out.println(setAt(n)); } } private static void init() { set.add(1); int n = 1; int loop = 1; while(set.size() < N){ add2set(n); n = setAt(++ loop); } } private static int setAt(int p) { int n = 0; Iterator<Integer> it = set.iterator(); int j = 1; while(it.hasNext()){ n = it.next(); if(j == p) return n; j ++; } return n; } private static void add2set(int n) { set.add(n * 2); set.add(n * 3); set.add(n * 5); } }