Poj Solution 1491

http://poj.org/problem?id=1491

//* @author ������<hongxp11@163.com>
import java.text.DecimalFormat;
import java.util.Scanner;
import java.util.Vector;

public class Main {

    public static int factor(int a, int b) {
    if (b == 0)
        return a;
    else
      return factor(b, a % b);

    }

public static void main(String[] args) {
  // TODO Auto-generated method stub
 Scanner in = new Scanner(System.in);
  while (true) {
    int n = in.nextInt();
    if (n == 0)
        break;
    int[] array = new int[n];
    for (int i = 0; i < n; i++) {
        array[i] = in.nextInt();
    }
    int total = (n - 1) * n / 2;
    int count = 0;
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            if (factor(array[i], array[j]) == 1)
                count++;
        }
    }
    if (count == 0)
        System.out.println("No estimate for this data set.");
    else {
        double pi = Math.sqrt(6.0 * total / count);
        DecimalFormat output = new DecimalFormat("#.######");
        System.out.println(output.format(pi));
    }
   }
 }

}