// Tyler Mi
// Showing an application of recursion, brute-force exploring
// of possibilities
import java.util.*;

public class RecursiveBacktracking {
   public static void main(String[] args) {
      fourAB();
      diceRoll(2);
   }
   
   // Prints all strings of length 4 consisting of a's and b's
   public static void fourAB() {
      fourABHelper("");
   }
   
   // Prints all strings of length 4 consisting of a's and b's
   // that start with the given prefix "accumulator"
   private static void fourABHelper(String accumulator) {
      if (accumulator.length() == 4) {
         System.out.println(accumulator);
      } else {
         fourABHelper(accumulator + "a");
         fourABHelper(accumulator + "b");
      }
   }
   
   // Assumes that n >= 0
   // Prints all possible outcomes of rolling the given number of
   // 6-sided dice in the format [#, #, #]
   public static void diceRoll(int n) {
      diceRollHelper(new ArrayList<>(), n);
   }
   
   // prints all possible outcomes of rolling the given number of
   // 6-sided dice in the format [#, #, #] with chosen as the rolls
   // that have already been computed
   private static void diceRollHelper(List<Integer> chosen, int remaining) {
      if (remaining == 0) { // Success
         System.out.println(chosen);
      } else {              // In-Bounds
         for (int i = 1; i <= 6; i++) {            // for choice we have
            chosen.add(i);                         // choose
            diceRollHelper(chosen, remaining - 1); // explore
            chosen.remove(chosen.size() - 1);      // unchoose
         }
      }
   }
}