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Towers of Hanoi implementation using stack.

The Tower of Hanoi is a mathematical game or puzzle. It consists of three rods, and a number of disks of different sizes which can slide onto any rod. The puzzle starts with the disks in a neat stack in ascending order of size on one rod, the smallest at the top, thus making a conical shape. The objective of the puzzle is to move the entire stack to another rod, obeying the following rules:

1) Only one disk must be moved at a time.

2) Each move consists of taking the upper disk from one of the rods and sliding it onto another rod, on top of the other disks that may already be present on that rod.

3) No disk may be placed on top of a smaller disk.

In this example, we are solving it by using stacks.

package com.java2novice.ds.stack;

public class TowersOfHanoiImpl {
	private static MyDynamicStack[] tower; 
	public static void towersOfHanoi(int n) {

		// create three stacks, tower[0] is scratch
		tower = new MyDynamicStack[4];
		for (int i = 0; i <= 3; i++){
			tower[i] = new MyDynamicStack(4);
		for (int d = n; d > 0; d--){
			// initialize
			// add disk d to tower 1
			tower[1].push(new Integer(d)); 
		// move n disks from tower 1 to 2 using 3 as
		// intermediate tower
		showTowerStates(n, 1, 2, 3);

	public static void showTowerStates(int n, int x, int y, int z) {
		if (n > 0) {
				showTowerStates(n - 1, x, z, y);
				// move d from top of tower x
				Integer d = (Integer) tower[x].pop(); 
				// to top of tower y
				System.out.println("Move disk " + d 
						+ " from tower "+ x + " to top of tower " + y);
				showTowerStates(n - 1, z, y, x);
			} catch(Exception ex){}

	public static void main(String[] args) {
		System.out.println("Running 3 disk problem:");

public class MyDynamicStack {

	private int stackSize;
	private int[] stackArr;
	private int top;

	 * constructor to create stack with size
	 * @param size
	public MyDynamicStack(int size) {
		this.stackSize = size;
		this.stackArr = new int[stackSize]; = -1;

	 * This method adds new entry to the top 
	 * of the stack
	 * @param entry
	 * @throws Exception 
	public void push(int entry){
			System.out.println(("Stack is full. Increasing the capacity."));
		this.stackArr[++top] = entry;

	 * This method removes an entry from the 
	 * top of the stack.
	 * @return
	 * @throws Exception 
	public int pop() throws Exception {
			throw new Exception("Stack is empty. Can not remove element.");
		int entry = this.stackArr[top--];
		return entry;
	 * This method returns top of the stack
	 * without removing it.
	 * @return
	public long peek() {
		return stackArr[top];

	private void increaseStackCapacity(){
		int[] newStack = new int[this.stackSize*2];
		for(int i=0;i<stackSize;i++){
			newStack[i] = this.stackArr[i];
		this.stackArr = newStack;
		this.stackSize = this.stackSize*2;
	 * This method returns true if the stack is 
	 * empty
	 * @return
	public boolean isStackEmpty() {
		return (top == -1);

	 * This method returns true if the stack is full
	 * @return
	public boolean isStackFull() {
		return (top == stackSize - 1);

	public static void main(String[] args) {
		MyDynamicStack stack = new MyDynamicStack(2);
		for(int i=1;i<10;i++){
		for(int i=1;i<4;i++){
			try {
			} catch (Exception e) {
				// TODO Auto-generated catch block

Running 3 disk problem:
Move disk 1 from tower 1 to top of tower 2
Move disk 2 from tower 1 to top of tower 3
Move disk 1 from tower 2 to top of tower 3
Move disk 3 from tower 1 to top of tower 2
Move disk 1 from tower 3 to top of tower 1
Move disk 2 from tower 3 to top of tower 2
Move disk 1 from tower 1 to top of tower 2
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List of Stack Data Structure Examples

  1. Stack introduction & implementation
  2. Java Dynamic Stack Implementation
  3. Stack implementation using generics bounded type.
  4. Reverse a word or string using Stack data structure.
  5. Write a program to find out delimiter matching using stack.
  6. Convert a decimal into a binary number using stack.
  7. Towers of Hanoi implementation using stack.
  8. Evaluation of an infix expression that is fully parenthesized using stack in java.
Knowledge Centre
wait Vs sleep methods
sleep(): It is a static method on Thread class. It makes the current thread into the "Not Runnable" state for specified amount of time. During this time, the thread keeps the lock (monitors) it has acquired.

wait(): It is a method on Object class. It makes the current thread into the "Not Runnable" state. Wait is called on a object, not a thread. Before calling wait() method, the object should be synchronized, means the object should be inside synchronized block. The call to wait() releases the acquired lock.
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-- Winston Churchill

About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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