import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author René Moll (188084), Philipp Mehlhorn (188308)
 *
 */
public class Truthtable {
    static ArrayList<String> array = new ArrayList<String>();
    static int counter = 0;

    private static void printTruthTable(int n) {
        //stopwatch start time
        double zstVorher = System.currentTimeMillis();
        n *= 2;

        int rows = (int) Math.pow(2, n);

        String tempString = "";

        // main for-loop. calculates every possible combination with Ds and Us for a specific length
        for (int i = 0; i < rows; i++) {
            for (int j = n - 1; j >= 0; j--) {
                // turns it into binary
                int temp = i / (int) Math.pow(2, j) % 2;
                // converts it into Ds and Us and saves it into a temporary string
                tempString = tempString.concat((temp == 1) ? "U" : "D");
            }
            // every temporary string gets sent to the checkstring method to get checked
            if (tempString != "")
                checkString(tempString);
            tempString = "";
        }

        for (String s : array) {
            System.out.println(s);
        }

        //stopwatch end time
        double zstNachher = System.currentTimeMillis();
        System.out.println("\nZeit benötigt: " + ((zstNachher - zstVorher)) + " msec oder  "
                + ((zstNachher - zstVorher) / 1000) + " Sekunden");
        System.out.println(counter + " Möglichkeiten für n=" + n / 2 + " (" + n + " Stellen)");
    }


    // checks the string for the rules that the excercise gave us
    public static void checkString(String s) {
        if ((s.contains("DUDUDU") && (countDUDU(s, "DUDU") <= 1))
                || (((countDUDU(s, "DUDU") == 2)) && !(s.contains("DUDUDU")))) {

            if (s.startsWith("U") && s.endsWith("D")) {
                if (checkAmountDU(s)) {
                    if (countDUDU(s, "D") == countDUDU(s, "U")) {
                        //if the path fullfills every rule, than it gets saved in an string array
                        counter++;
                        array.add(s);
                    }
                }
            }
        }
    }

    /**
     * Counts the amount of search patterns in a string
     * @param s the string that should be checked
     * @param search the search pattern, that will be counted
     * @return amount of the search string value in the string
     */
    public static int countDUDU(String s, String search) {

        Pattern p = Pattern.compile(search);
        Matcher m = p.matcher(s);
        int count = 0;
        while (m.find()) {
            count += 1;
        }
        return count;
    }


    /**
     * @param s a DU path to check
     * @return boolean true,if there are always more or equal Us than Ds
     */
    public static boolean checkAmountDU(String s) {
        for (int i = 1; i <= s.length(); i++) {
            if (!(countDUDU(s.substring(0, i), "D") <= countDUDU(s.substring(0, i), "U"))) {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        // hier dein tatsächliches n angeben ! (n=5 hat 3 Möglichkeiten und 10 Stellen z.B.)
        printTruthTable(15);
    }

}