SinglyLinkedList.java

import java.util.Scanner;
public class SinglyLinkedList {
    class Node{
        int data;   //value
        Node next;   //address of the next node

        Node(int data){
            this.data=data;
            this.next=null;
        }}
    Node head;  //points to the first node
    int size;   //total nodes

public void insertFront(int data){
    Node newNode = new Node(data);    //creating a new node for operations
    newNode.next=head;   //linking it to the current node
    head=newNode;   //make the newNode the new head
    size++;    //time complexity is O(1)
}

public void insertEnd(int data) {
    Node newNode = new Node(data);
    if (head == null) {
        head = newNode;
        size++;
        return;
    }
    Node temp = head;
    while (temp.next != null) {
        temp = temp.next;
    }
    temp.next = newNode;
    size++;
}

public void insertPosition(int data, int pos) {
    if (pos < 1) {
        System.out.println("Invalid position.");
        return;
    }
    Node newNode = new Node(data);
    if (pos == 1) {
        newNode.next = head;
        head = newNode;
        size++;
        return;
    }
    Node temp = head;
    for (int i = 1; i < pos - 1 && temp != null; i++) {
        temp = temp.next;
    }
    if (temp == null) {
        System.out.println("Position out of bounds!");
        return;
    }
    newNode.next = temp.next;
    temp.next = newNode;
    size++;
}

public void display() {
    Node temp = head;
    while (temp != null) {
        System.out.print(temp.data + " -> ");
        temp = temp.next;
    }
    System.out.println("NULL");
    System.out.println("Size is "+size);
}
public Node get(int index){
    Node node = head;
    for (int i = 0; i < index; i++) {
        node = node.next;
    }
    return node;
}

public void deleteFirst(){
    if (head==null){
        System.out.println("List already empty.");
        return; }
    int val = head.data;
    System.out.println("Deleted: "+val);
    head=head.next;
    size--;
}

public void deleteLast(){
    if(size<=1){
        deleteFirst();
    }
    if (head.next == null) {
        System.out.println("Deleted: " + head.data);
        head = null;
        return;
    }
    Node temp=head;
    while(temp.next.next!=null){
        temp=temp.next; }
    System.out.println("Deleted: "+temp.next.data);
    temp.next=null;
    size--;
    }

public void deletePosition(int pos){
    if(head==null){
        System.out.println("List is empty.");
        return;
    }
    if(pos==0){
        System.out.println("Deleted: "+head.data);
        head=head.next;
        size--;
        return;
    }
    if (pos < 0 || pos >= size) {
        System.out.println("Invalid position!");
        return;
    }
    Node prev=head;
    for (int i = 0; i < pos-1; i++) {
        prev=prev.next;
    }
    Node toDel=prev.next;
    System.out.println("Deleted: "+toDel.data);
    prev.next=toDel.next;
    size--;
    }

public static void main(String[] args) {
    SinglyLinkedList list = new SinglyLinkedList();
        Scanner sc = new Scanner(System.in);
        int choice;
        do{
        System.out.println("Enter 1 for inserting at the front\n2 for inserting at the end\n3 for inserting in the middle\n4 to delete at the beginning\n5 to delete at the end\n6 to delete at a position\n7 to display\n8 to exit: ");
        choice = sc.nextInt();
        switch (choice) {
            case 1:
                System.out.print("Enter value to insert: ");
                int val1 = sc.nextInt();
                list.insertFront(val1);
                break;
            case 2:
                System.out.print("Enter value to insert: ");
                int val2 = sc.nextInt();
                list.insertEnd(val2);
                break;
            case 3:
                System.out.println("Enter the value to insert: ");
                int val3 = sc.nextInt();
                System.out.println("Enter the position to insert at: ");
                int pos = sc.nextInt();
                list.insertPosition(val3, pos);
                break;
            case 4:
                list.deleteFirst();
                break;
            case 5:
                list.deleteLast();
                break;
            case 6:
                System.out.println("Enter position to delete that node: ");
                int index= sc.nextInt();
                list.deletePosition(index-1);
                break;
            case 7:
                list.display();
                break;
            case 8:
                System.out.println("Exit code...");
                break;
            default:
                System.out.println("Invalid choice.");
        }} while(choice!=8);

}}