// Hunter Schafer, CSE 143
// Examples of recursive backtracking

import java.util.*;

public class Backtracking {
    public static void main(String[] args) {
        fourAB();
        diceRoll(3);
    }

    // This method will print all strings of length 4 composed of
    // only a's and b's
    public static void fourAB() {
        fourAB("");
    }

    // Prints all strings of length 4 composed of only a's and b's
    // that start with the given prefix soFar
    private static void fourAB(String soFar) {
        if (soFar.length() == 4) {
            System.out.println(soFar);
        } else {
            // soFar = "a"
            // choose an "a", now result is "aa"
            fourAB(soFar + "a");
            fourAB(soFar + "b");
        }
    }

    // Prints all possible outcomes of rolling the given
    // number of six-sided dice in [#, #, #] format.
    // pre: dice >= 0
    public static void diceRoll(int dice) {
        diceRoll(dice, new ArrayList<Integer>());
    }

    // Prints all possible outcomes of rolling the given number
    // of six-sided dice in [#, #, #] format with chosen
    // as the prefix of all printed.
    private static void diceRoll(int dice, List<Integer> chosen) {
        if (dice == 0) {
            System.out.println(chosen);
        } else {
            for (int i = 1; i <= 6; i++) {     // for all possible choices
                chosen.add(i);                      // choose
                diceRoll(dice - 1, chosen);         // explore
                chosen.remove(chosen.size() - 1);   // unchoose
            }
        }
    }
}