lec69_implementation_LL_stack.java

package shreya.java;

import java.util.Stack;

public class lec69_implementation_LL_stack {
    public static class Node{  //user defined data type
        int val;
        Node next;
        Node(int val){
            this.val =val;
        }
    }
    public static class LLStack{  //user defined data structure
        Node head = null;
        int size =0;
        void push(int x){
            Node temp = new Node(x);
            temp.next = head;
            head = temp;
            size++;
        }
        int pop(){
            if(head==null){
                System.out.println("stack is empty");
                return -1;
            }
            int x = head.val;
            head = head.next;
            return x;
        }
        int peek(){
            if(head == null){
                System.out.println("Stack is empty");
                return -1;
            }
            return head.val;
        }
        void displayrec(Node h){
            if(h==null)return;
            displayrec(h.next);
            System.out.print(h.val+" ");
        }

        void display(){
            displayrec(head);
            System.out.println();
        }

        int size(){  //getter
            return size;
        }
        boolean isEmpty(){
            if(size==0)return true;
            return false;
        }

    }
    public static void main(String[] args) {
        LLStack st = new LLStack();
        st.push(4);
        st.push(3);
        st.push(1);
         st.push(5);
      //  st.push(9);
        st.display();
        System.out.println(st.pop());
        st.display();
        System.out.println(st.peek());
        st.display();
        System.out.println(st.size());


    }
}