

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) {
try{
showTowerStates(n  1, x, z, y);
// move d from top of tower x
Integer d = (Integer) tower[x].pop();
// to top of tower y
tower[y].push(d);
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:");
towersOfHanoi(3);
}
}
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];
this.top = 1;
}
/**
* This method adds new entry to the top
* of the stack
* @param entry
* @throws Exception
*/
public void push(int entry){
if(this.isStackFull()){
System.out.println(("Stack is full. Increasing the capacity."));
this.increaseStackCapacity();
}
this.stackArr[++top] = entry;
}
/**
* This method removes an entry from the
* top of the stack.
* @return
* @throws Exception
*/
public int pop() throws Exception {
if(this.isStackEmpty()){
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++){
stack.push(i);
}
for(int i=1;i<4;i++){
try {
stack.pop();
} catch (Exception e) {
// TODO Autogenerated catch block
e.printStackTrace();
}
}
}
}


Output: 
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





List of Stack Data Structure Examples
 Stack introduction & implementation
 Java Dynamic Stack Implementation
 Stack implementation using generics bounded type.
 Reverse a word or string using Stack data structure.
 Write a program to find out delimiter matching using stack.
 Convert a decimal into a binary number using stack.
 Towers of Hanoi implementation using stack.
 Evaluation of an infix expression that is fully parenthesized using stack in java.



What is wrapper class?
Everything in java is an object, except primitives. Primitives are
int, short, long, boolean, etc. Since they are not objects, they cannot
return as objects, and collection of objects. To support this, java provides
wrapper classes to move primitives to objects. Some of the wrapper classes
are Integer, Long, Boolean, etc.
The greatest obstacle to discovery is not ignorance; it is the illusion of knowledge.
 Daniel J. Boorstin
