Question

Problem 2: based on java.util.LinkedList class, create MyStack class that should have the methods: push(), pop(), peek(), size(), isEmpty().

my linkedlist class is:

public class Lab8_problem1 {
   private Node head, tail;
private int size;
  
public Lab8_problem1() {
this.head = null;
this.tail = null;
this.size = 0;
}
//Insert a node at specifc Location
public void insertAt(int value, int index)
{
Node newNode = new Node();
newNode.data = value;
if(head == null){
head = newNode;
tail = newNode;
head.next = null;
tail.next = null;
}
else
{
if(index == 0)
insertFront(value);
else if(index == size)
insertLast(value);
else if(index > size)
System.out.println("Cannot insert");
else{
  
int count = 0;
Node p1 = head.next;
Node p2 = head;
while(count <index)
{
p1 = p1.next;
p2 = p2.next;
count++;
}
newNode.next = p1;
p2.next = newNode;
}
}
size++;
}
//Insert a node at the end of the list
public void insertLast(int value)
{
Node newNode = new Node();
newNode.data = value;
if(head == null){
head = newNode;
tail = newNode;
head.next = null;
tail.next = null;
}
else
{
tail.next = newNode;
tail = newNode;
}
size++;
}
//Insert a node at the front of the list
public void insertFront(int value)
{
Node newNode = new Node();
newNode.data = value;
if(head == null){
head = newNode;
tail = newNode;
head.next = null;
tail.next = null;
}
else
{
newNode.next = head;
head = newNode;
}
size++;
}
//Display all nodes in the list
public void display()
{
if(head == null)
System.out.println("Empty List!");
else
{
Node pointer = head;
//while(pointer!=null)
for (int i = 0; i < size; i++) {
System.out.print(pointer.data + " ");
pointer = pointer.next;
}
System.out.println("");
}
}
//Method to check of the list is empty - isEmpty() (returns a Boolean)
public boolean isEmpty(){
return (head==null); //
}
//Method to return the size of the list
public int getSize(){
return size;
}
//Delete all nodes in the list
public void clear(){
head = null;
tail = null;
size = 0;
}
//Search List for a node with a certain value (returns the node if found, null if not found)
public Node search(int value)
{
if(head == null)
System.out.println("Empty List!");
else
{
Node pointer = head;
//while(pointer!=null)
for (int i = 0; i < size; i++) {
if(pointer.data==value) // if zero => they are equal
{
return pointer;
}
pointer = pointer.next;
}
}
return null;
}
//get node of specific index
public Node getNode(int index)
{
if(head == null || index > size-1)
System.out.println("Empty List or invalide index!");
else
{
Node pointer = head;
int count = 0;
while(count != index)
{
count++;
pointer = pointer.next;
}
return pointer;
}
return null;
}
//Delete a node with a specific value in the list if found
public void delete(int value){
if(isEmpty())
System.out.println("Empty List!!");
else if(head.data == value) // if zero => they are equal
{
head = head.next;
}
else{
Node pointer1 = head.next;
Node pointer2 = head;
  
while(pointer1!=null) {
if(pointer1.data==value) // if zero => they are equal
{
pointer2.next = pointer1.next;
if(tail.data==value)
tail = pointer2;
break;
}
pointer1 = pointer1.next;
pointer2 = pointer2.next;
}
}
size--;
}
//Delete a node with a specific value in the list if found
public void deleteAt(int index){
if(isEmpty() || index >= size)
System.out.println("Empty List or invalid index!!");
else if(index == 0) // if zero => they are equal
head = head.next;
  
else{
Node pointer1 = head.next;
Node pointer2 = head;
int count = 0;
while(pointer1!=null) {
  
if(count==index)
{
pointer2.next = pointer1.next;
if(index == size-1)
tail = pointer2;
break;
}
pointer1 = pointer1.next;
pointer2 = pointer2.next;
}
}
size--;
}

class Node {

public int data;
public Node next;
  
public Node() {
this.data = 0;
this.next = null;
}
public int getData(){
return data;
}

public int count(){
if(head==null)
return 0;
else return countR(head);
}
private int countR(Node p){
if(p==null)
return 0;
else
{
if(p.data<0)
return 1+countR(p.next);
else
return 0+countR(p.next);
}
}
public int maxNum(){
return maxNumR(head, head.data);
}
public int maxNumR(Node p, int max){
if(p==null)
return max;
else{
if(p.data>max)
return maxNumR(p.next, p.data);
else
return maxNumR(p.next, max);
  
}
}
public void printR(Node p){
if(p==null);
else{
System.out.print(p.data+"\t");
printR(p.next);
}
}
public void printReve(){
printReveR(head);
}
private void printReveR(Node p){
if(p==null);
else{
printReveR(p.next);
System.out.print(p.data+"\t");
}
}
public void searchIndex(int value){
if(head==null)
System.out.println("empty");
else
searchIndexR(value, head, 0);
}
private void searchIndexR(int value, Node p, int i){
if(p==null);
else{
if(value == p.data)
System.out.print(i+"\t");
searchIndexR(value, p.next, ++i);
}
}
}
}

java - netbeans.

Answer 1

The question says to develop a stack using java.util.LinkedList, I don’t think it needs to use the linked list class provided by you. Anyway, I have written two solutions (using both approaches). Choose whichever you want.

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

Note: the stack is integer based, not generic, if you want it to be generic, let me know.

// Stack.java using the linked list class you provided

public class Stack {

      // creating an object of Lab8_problem1 as instance variable

      private Lab8_problem1 list;

      // constructor

      public Stack() {

            // initializing list

            list = new Lab8_problem1();

      }

      // adds an element to the top of stack

      public void push(int value) {

            // here we consider front of list as top of stack, adding value to front

            list.insertFront(value);

      }

      // removes and returns the top element from stack

      public int pop() {

            // if empty, throwing an exception

            if (isEmpty()) {

                  throw new RuntimeException("Stack is empty!");

            }

            // getting element at index 0 from stack (front of list)

            int element = list.getNode(0).data;

            // removing it

            list.deleteAt(0);

            // returning removed element

            return element;

      }

      // returns the top element from stack

      public int peek() {

            if (isEmpty()) {

                  throw new RuntimeException("Stack is empty!");

            }

            // returning element at index 0 from stack (front of list)

            return list.getNode(0).data;

      }

      // returns the size of the list

      public int size() {

            return list.getSize();

      }

      // returns true if stack is empty

      public boolean isEmpty() {

            return size() == 0;

      }

}

// Stack.java using java.util.LinkedList

import java.util.LinkedList;

public class Stack {

      // creating an object of java.util.LinkedList as instance variable

      private LinkedList<Integer> list;

      // constructor

      public Stack() {

            // initializing list

            list = new LinkedList<Integer>();

      }

      // adds an element to the top of stack

      public void push(int value) {

            // here we consider front of list as top of stack, adding value to front

            list.addFirst(value);

      }

      // removes and returns the top element from stack

      public int pop() {

            // if empty, throwing an exception

            if (isEmpty()) {

                  throw new RuntimeException("Stack is empty!");

            }

            // getting element at index 0 from stack (front of list)

            int element = list.get(0);

            // removing it

            list.removeFirst();

            // returning removed element

            return element;

      }

      // returns the top element from stack

      public int peek() {

            if (isEmpty()) {

                  throw new RuntimeException("Stack is empty!");

            }

            // returning element at index 0 from stack (front of list)

            return list.getFirst();

      }

      // returns the size of the list

      public int size() {

            return list.size();

      }

      // returns true if stack is empty

      public boolean isEmpty() {

            return size() == 0;

      }

}