Calculate the number of possible draws in the draw for the round of 16 in the 2012–13 UEFA Champions League; see http://math.stackexchange.com/questions/262629.

Question262629.java

public class Question262629 {
    final static String [] [] associations =
    {
        {"FRA","GER","SPA","GER","ITA","GER","SPA","ENG"},
        {"POR","ENG","ITA","SPA","UKR","SPA","SCO","TUR"}
    };

    static int count;
    static boolean [] paired = new boolean [8];

    public static void main (String [] args) {
        recurse (0);
        System.out.println (count);
    }

    static void recurse (int n) {
        if (n == 8)
            count++;
        else
            for (int i = 0;i < 8;i++)
                if (i != n && !paired [i] && !associations [0] [n].equals (associations [1] [i])) {
                    paired [i] = true;
                    recurse (n + 1);
                    paired [i] = false;
                }
    }
}