/** * an iterative solution to the Towers of Hanoi */import java.lancs.* ;class PegException extends Exception    {    public PegException() {}    }class Peg    {    private static final int MAX_NO_DISKS = 100 ;    private String name ;    private int[] disks = new int[MAX_NO_DISKS] ;    private int noDisks ;    public Peg successor ;    public Peg(String n)	{	name = n ;	noDisks = 0 ;	} // end of constructor method    public String toString()	{	return name ;	} // end of method toString    public int remove() throws PegException	{	if (noDisks == 0)	    throw new PegException() ;	int temp = disks[noDisks - 1] ;	noDisks-- ;	return temp ;	} // end of method remove    public void add(int d)	{	disks[noDisks] = d ;	noDisks++ ;	} // end of method add    public int top()	{	if (noDisks == 0)	    return  MAX_NO_DISKS + 1 ;	return disks[noDisks - 1] ;	} // end of method top    public int noOfDisks()	{	return noDisks ;	} // end of method noOfDisks    } // end of class Pegpublic class Chapter18n4    {    static int noMoves ;    public static void main(String[] args) throws Exception	{	Peg pegA = new Peg("A"),	    pegB = new Peg("B"),	    pegC = new Peg("C") ;	BasicIo.prompt("number of disks? ") ;	int n = BasicIo.readInteger() ;	for (int i = 0 ; i < n ; i++)	    pegA.add(n - i) ;	noMoves = 0 ;	hanoi(n, pegA, pegB, pegC) ;	System.out.println("\nno of moves for " + n + " disks is " + noMoves) ;	} // end of main method    public static void moveDisk(Peg fromPeg, Peg toPeg)        {	try {	    int d = fromPeg.remove() ;	    toPeg.add(d) ;	    System.out.println("Move disk " + d + " from " + fromPeg +							" to " + toPeg) ;	    noMoves++ ;	    }	catch(PegException e)	    {	    System.out.println("major peg problem") ;	    System.exit(1) ;	    }	} // end of method moveDisk    public static void hanoi(int n, Peg fromPeg, Peg toPeg, Peg helpPeg)	{	if (n % 2 == 1)	    {	    fromPeg.successor = toPeg ;	    toPeg.successor = helpPeg ;	    helpPeg.successor = fromPeg ;	    }	else	    {	    fromPeg.successor = helpPeg ;	    helpPeg.successor = toPeg ;	    toPeg.successor = fromPeg ;	    }	while (true)	    {	    Peg smallest = fromPeg ;	    if (toPeg.top() < smallest.top())		smallest = toPeg ;	    if (helpPeg.top() < smallest.top())		smallest = helpPeg ;	    Peg newSmallest = smallest.successor ;	    Peg otherPeg = newSmallest.successor ;	    moveDisk(smallest, newSmallest) ;	    if (toPeg.noOfDisks() == n)		break ;	    if (smallest.top() < otherPeg.top())		moveDisk(smallest, otherPeg) ;	    else		moveDisk(otherPeg, smallest) ;	    }	} // end of method hanoi    } // end of class Chapter18n4