Linked List: Program to implement a stack using linked list

Write a program to implement a stack like data structure using linked list

Stack is a data structure that follows LIFO (last in first out) rule
For implementing the stack using a linked list we will perform all operations of the stack

• push(): it pushes the given element into the stack
• peek(): this operation returns the element which is at the top(an element that enters last)
• pop(): this operation deletes the top element of the stack
• display(): this operation simply displays all elements of the stack

• We implement the above operations on a LinkedList such that we derive the LIFO property of the stack
• push(): add elements to the head of LinkedList
• pop(): remove elements from the head of LinkedList
• peek(): show a head element of LinkedList
• display(): iterate LinkedList from head and print elements

Approach

1. push()

   • Create new node current and current.data = given element
   • If the current is NULL then the stack is full/overflow so, cannot push
   • Else make current.next = top
   • And set-top on current

2. peek()

   • If top is NULL then the print stack is empty and simply returns
   • Else return top.data

3. pop()

   • If top is NULL then the print stack is empty and simply returns
   • Else set top = top.next

4. display()

   • If top is NULL then simply return
   • Create a pointer say current and point on top
   • Print all elements of stack till current is not NULL

Complexity

Time Complexity : O(1)
Space Complexity : O(n) , where n is the size of linked list

Java Code

class LinkedListAsStack{
	
        class Node {
            int data;
            Node next;
         
            Node(int d) {
                this.data = d;
                this.next = null;
            }
        }
    
        Node top;
     
        public void push(int element) {
            Node current = new Node(element);
            current.next = top;
            top = current;
        }
     
        public int peek() {
            if (top == null) {
                System.out.println("Stack is Empty");
                return -1;
            } else {
                return top.data;
            }
        }
     
        public void pop() {
            if (top == null) {
                System.out.println("Stack is Empty");
                return;
            } else {
                top = top.next;
            }
        }
     
        public void display() {
            if (top == null) {
                System.out.println("Stack is Empty");
                return;
            }
            Node current = top;
            while (current != null) {
                System.out.print(current.data + "\n");
                current = current.next;
            }
        }
     
        public static void main(String[] args) {
            LinkedListAsStack ss = new LinkedListAsStack();
            ss.push(10);
            ss.push(20);
            ss.push(30);
            ss.push(40);
            ss.push(50);
            ss.push(60);
            System.out.println("Element at peek in the stack is " + ss.peek());
            System.out.println("Original Stack");
            ss.display();
            System.out.println("Stack after pop operation");
            ss.pop();
            ss.display();
        }
    
 }

Output

Element at peek in the stack is 60
Original Stack
60
50
40
30
20
10
Stack after pop operation
50
40
30
20
10