/** 
  * A program to solve the towers of Hanoi puzzle
  * @author         Edo Biagioni
  * @lecture        ICS 211 March 8 (or later)
  * @date           March 3, 2011
  */

import javax.swing.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;

public class Towers {

  public Towers() {
    super();
  }

  public static String toString(int[] t1, String t1name, int[] t2,
                                String t2name, int[] t3, String t3name) {
    String result = t1name + ": ";
    for (int index = 0; index < t1.length && t1[index] != 0; index++) {
      result += t1[index] + ", ";
    }
    result += t2name + ": ";
    for (int index = 0; index < t2.length && t2[index] != 0; index++) {
      result += t2[index] + ", ";
    }
    result += t3name + ": ";
    for (int index = 0; index < t3.length && t3[index] != 0; index++) {
      result += t3[index] + ", ";
    }
    return result;
  }

  /* @throws ArrayOutOfBoundsException if t1 does not have any
   *         disks or if t2 has no room.
   */
  private static void moveTop(int[] t1, String t1name,
                              int[] t2, String t2name) {
    int diskIndex1 = t1.length - 1;
    while (t1[diskIndex1] == 0) {  // may throw exception
      diskIndex1--;
    }
    int move = t1[diskIndex1];
    int diskIndex2 = 0;
    int smallest = -1;
    while (t2[diskIndex2] != 0) {  // may throw exception
      smallest = t2[diskIndex2];
      diskIndex2++;
    }
    if ((smallest != -1) && (smallest <= move)) {
      System.out.println("illegal move of disk of size " + move +
                         " onto disk of size " + smallest);
    }
    // at this point, t1[diskIndex1] == move != 0 and t2[diskIndex2] == 0
    System.out.println("moving disk of size " + move +
                       " from " + t1name + " to " + t2name);
    t2[diskIndex2] = t1[diskIndex1];
    t1[diskIndex1] = 0;
  }

  /* move n disks from tower 1 to tower2 using tower3 if necessary
   * @param the disk sizes on the first tower
   * @param the disk sizes on the second tower
   * @param the disk sizes on the third tower
   * @result the new disk sizes in the parameter arrays
   * @prints the moves to make
   */
  public static void solveTowers(int n, int[] t1, String t1name, int[] t2,
                                 String t2name, int[] t3, String t3name) {
    /* System.out.println("at start of solveTowers: " +
                       toString(t1, t1name, t2, t2name, t3, t3name)); */
    if (n == 1) {
      moveTop(t1, t1name, t2, t2name);
    } else {
      // move the n-1 disks from t1 to t3 using t2
      solveTowers(n - 1, t1, t1name, t3, t3name, t2, t2name);
      // move the nth disk from t1 to t2
      moveTop(t1, t1name, t2, t2name);
      // move the n-1 disks from t3 to t2 using t1
      solveTowers(n - 1, t3, t3name, t2, t2name, t1, t1name);
    }
    /* System.out.println("at end of solveTowers: " +
                       toString(t1, t1name, t2, t2name, t3, t3name)); */
  }

  /** 
    * unit test method -- run the towers of hanoi program
    * @param one parameter specifies the number of disks
    */
  public static void main (String [] arguments) {
    int disks = 8;
    if (arguments.length == 1) {
      disks = Integer.parseInt(arguments[0]);
    }
    int[] tower1 = new int[disks];
    int[] tower2 = new int[disks];
    int[] tower3 = new int[disks];
    for (int i = 0; i < disks; i++) {
      tower1[i] = disks - i;  // diameter of the disk
      tower2[i] = 0;          // no disk
      tower3[i] = 0;          // no disk
    }
    // move from tower1 to tower2 using tower3 as a spare
    solveTowers(disks, tower1, "tower1", tower2, "tower2", tower3, "tower3"); 
  }

}

/* sample run:
    $ java Towers 4
    moving disk of size 1 from tower1 to tower3
    moving disk of size 2 from tower1 to tower2
    moving disk of size 1 from tower3 to tower2
    moving disk of size 3 from tower1 to tower3
    moving disk of size 1 from tower2 to tower1
    moving disk of size 2 from tower2 to tower3
    moving disk of size 1 from tower1 to tower3
    moving disk of size 4 from tower1 to tower2
    moving disk of size 1 from tower3 to tower2
    moving disk of size 2 from tower3 to tower1
    moving disk of size 1 from tower2 to tower1
    moving disk of size 3 from tower3 to tower2
    moving disk of size 1 from tower1 to tower3
    moving disk of size 2 from tower1 to tower2
    moving disk of size 1 from tower3 to tower2
 */