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);
	}

}