/**

* @author Varun Upadhyay (https://github.com/varunu28)

*/

// An implementation of a Stack using a Linked List

class StackOfLinkedList {

public static void main(String[] args) {

LinkedListStack stack = new LinkedListStack();

stack.push(1);

stack.push(2);

stack.push(3);

stack.push(4);

stack.push(5);

stack.printStack();

System.out.println("Size of stack currently is: " + stack.getSize());

stack.pop();

stack.pop();

System.out.println("Top element of stack currently is: " + stack.peek());

}

}

// A node class

class Node {

public int data;

public Node next;

public Node(int data) {

this.data = data;

this.next = null;

}

}

/**

* A class which implements a stack using a linked list

* <p>

* Contains all the stack methods : push, pop, printStack, isEmpty

**/

class LinkedListStack {

Node head = null;

public void push(int x) {

Node n = new Node(x);

if (head == null) {

head = n;

} else {

Node temp = head;

n.next = temp;

head = n;

}

}

public void pop() {

if (head == null) {

System.out.println("Empty stack. Nothing to pop");

}

Node temp = head;

head = head.next;

System.out.println("Popped element is: " + temp.data);

}

public int peek() {

if (head == null) {

return -1;

}

return head.data;

}

public void printStack() {

Node temp = head;

System.out.println("Stack is printed as below: ");

while (temp != null) {

if (temp.next == null) {

System.out.print(temp.data);

} else {

System.out.print(temp.data + " -> ");

}

temp = temp.next;

}

System.out.println();

}

public boolean isEmpty() {

return head == null;

}

public int getSize() {

if (head == null)

return 0;

else {

int size = 1;

Node temp = head;

while (temp.next != null) {

temp = temp.next;

size++;

}

return size;

}

}

}