/*
 * Kyle Pierce
 * CSE 143
 *
 * Examples of recursive backtracking
 */

import java.util.*;

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

   // post: prints all strings of length 4 containing only a's and b's
   public static void fourAB() {
      fourAB("");
   }

   // post: prints all strings of length 4 containing 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 {
         // recall that (soFar + "a") passes a new string as parameter
         // with an 'a' added to the end, but does not update the value
         // of soFar (since we did +, not +=), so we don't have to 
         // remove the 'a' before making the second call
         fourAB(soFar + "a");
         fourAB(soFar + "b");
      }
   }

   // pre:  dice >= 0
   // post: prints all possible outcomes of rolling the given number of
   //       6-sided dice in the format [#, #, #]
   public static void diceRoll(int dice) {
      diceRoll(dice, new ArrayList<Integer>());
   }

   // post: 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 diceRoll(int dice, List<Integer> chosen) {
      if (dice == 0) {
         System.out.println(chosen);
      } else {            
         for (int i = 1; i <= 6; i++) {
            chosen.add(i);                      // choose
            diceRoll(dice - 1, chosen);         // explore
            chosen.remove(chosen.size() - 1);   // unchoose
         }
      }
   }
}