implementOfLL.java

//Question: Implementation of Linked List ~ Making a new class (LinkedList). Initialise and use various methods to do many tasks (Like insert, diplay, deletion) in Linked list.
package LinkedList;

import java.util.Scanner;

public class implementOfLL {

    public static class Node {       // Making new class named "Node"
        int val;      // Has part (Data)
        Node next;    // Has part (Next node reference)
    }

    public static class LinkedList {
        Node head;    // Has part
        Node tail;    // Has part
        int size;     // Has part

        void createLinkList() { // Method 1: Creating a Linked List
            Scanner sc = new Scanner(System.in);
            System.out.println("Enter the number of elements: ");
            int n = sc.nextInt();
            System.out.println("Enter the elements of the link list: ");
            if (n == 0) {
                System.out.println("Empty list");
            } else {
                for (int i = 0; i < n; i++) {
                    int val = sc.nextInt();
                    insertAtEnd(val);
                }
            }
        }

        void insertAtEnd(int value) { // Method 2: To insert element in end.
            Node temp = new Node();  // Making a new temporary node 
            temp.val = value;
            if (head == null) {  // Empty list
                head = temp;
                tail = temp;
            } else {  // If the list is not empty
                tail.next = temp;  // tail -> last element ; Isliye humne tail-node ke bad temp-node ko link kar diya ('tail-node' ke andar pahle 'null address' store tha {tail.next = null} par ab 'tail-node' ke andar 'temp' ka 'address' store hai)
                tail = temp;       // ekbar last main temp link ho jane ke bad ab last element temp hai. Isliye ab naya tail -> temp hoga.
            }
            size ++;
        }

        void insertAtStart(int value) { // Method 3: To insert element at the start
            Node temp = new Node();
            temp.val = value;
            if (head == null) {  // Empty list
                head = temp;
                tail = temp;
            } else {  // If the list is not empty
                temp.next = head;  // head -> first element ; Isliye temp ko head se pahle rakh kar, temp ke sath head ko link kar diya.  
                head = temp;       // ekbar temp ko head se pahle link karne ke bad ab naya head(first node) temp hoga.   
            }
            size ++;
        }

        void insertAtAnyposition(int position, int value) { // Method 4: To insert at any position
            Node temp = new Node();
            temp.val = value;
            Node x = head;   // x is the shallow copy of the head
            for(int i = 0; i < position - 1; i++) {
                x = x.next;  // x ki position barti rahegi jab tak na wo given position ki pahle tak aa jaye 
            }

            if (position == 0) {
                insertAtStart(value);
                return;
            } else if(position == size - 1) {
                insertAtEnd(value);
                return;
            } else if(position > size || position < 0) {
                System.out.println("Invalid position/Index");
            } else {
                temp.next = x.next; // temp node ko x ke bad wale node ke pahle link kar diya.
                x.next = temp;      // x ke bad temp ko link kar diya. (x node -> temp node [with the value & in the given position] -> x ke bad wala node)
            }
            size ++;
        }

        void display() {  // Method 5: To display the linked list.
            Node temp = head;  // temp is a Shallow copy of head
            while(temp != null) {
                System.out.print(temp.val + " ");
                temp = temp.next;
            }
        }

        void reverse() {  // Method 6: To reverse the linked list
            Node prev = null;    // prev node (শুরুতে null, কারণ নতুন tail → null দেখাবে)
            Node curr = head;    // curr node (যেটা লিস্ট traverse করবে)
            tail = head;          // পুরানো head এখন tail হয়ে যাবে

            while (curr != null) {
                Node nextNode = curr.next; // পরের node আগে রেখে দাও (না হলে হারিয়ে যাবে)
                curr.next = prev;         // current node এর next কে prev এর দিকে point করাও
                prev = curr;              // prev কে সামনে এগিয়ে নাও (prev = curr)
                curr = nextNode;           // curr কে সামনে এগিয়ে নাও (curr = nextNode)
            }
            head = prev; // লুপ শেষ হলে prev হবে নতুন head
        }

        int getvalue(int index) {  // Method 7: To get a particular element from the linked list
            if (index == size - 1) {
                return tail.val;
            } else if (index == 0) {
                return head.val;
            } else if (index < 0 || index > size) {
                System.out.println("Invalid Index");
                return 0;
            } else {
                Node temp = head; // Shallow copy (points to the head node)
                for (int i = 0; i < index; i++) {
                    temp = temp.next;
                }
                return temp.val;
            }
        }

        void setvalue(int index , int value) {  // Method 8: To change the value of a particular element from the linked list
            if (index == size - 1) {
                tail.val = value;
            } else if (index == 0) {
                head.val = value;
            } else if (index < 0 || index > size) {
                System.out.println("Invalid Index");
            } else {
                Node temp = head; // Shallow copy (points to the head node)
                for (int i = 0; i < index; i++) {
                    temp = temp.next;
                }
                temp.val = value;
            }
        }

        void deleteAtEnd() {  // Method 9: To delete an element from the last of a linked list
            if (head == null) {
                System.out.println("Empty list");
            } else {
                Node temp = head;  // Shallow copy (points to the head node)
                for (int i = 0; i < size-2; i++) {
                    temp = temp.next;               // temp last node ke wale node (Second last) ko point karega
                }
                tail = temp;  // Ab naya "tail" (last node) -> "temp" hoga.
                tail.next = null;
                size --;
            }
        }

        void deleteAtStart() {  // Method 10: To delete an element from the Start of a linked list
            if (head == null) {
                System.out.println("Empty list");
            } else {
                head = head.next;
                size --;
            }
        }

        void deleteAtAnyposition(int position) {  // Method 11: To delete node from any position
            if (head == null) {
                System.out.println("Empty list");
            } else if (position == 0) {
                deleteAtStart();
                return;
            } else if (position == size - 1) {
                deleteAtEnd();
                return;
            } else {
                Node temp = head;  // Shallow copy (points to the head node)
                for (int i = 0; i < position - 1; i++) {
                    temp = temp.next;               // temp, given position ke pahle wale node ko point karega
                }
                temp.next = temp.next.next;  // given position wala node skip ho raha hai
                size --;
            }
        }
    }
    public static void main(String[] args) {  // Main method
        LinkedList ll = new LinkedList();  // Making the object of LinkedList class
        Scanner sc = new Scanner(System.in);
        int ch;
        do {
            System.out.println("--- CHOICES ---");
            System.out.println("1.CREATE");
            System.out.println("2.INSERT AT END");
            System.out.println("3.INSERT AT START");
            System.out.println("4.INSERT AT ANY POSITION");
            System.out.println("5.DISPLAY");
            System.out.println("6.REVERSE");
            System.out.println("7.GET");
            System.out.println("8.SET");
            System.out.println("9.DELETE AT END");
            System.out.println("10.DELETE AT START");
            System.out.println("11.DELETE AT ANY POSITION");
            System.out.println("12.EXIT");
            ch = sc.nextInt();

            switch (ch) {
                case 1:
                ll.createLinkList();
                System.out.println("Linked List created.");
                break;
                case 2:
                System.out.print("Enter the value: ");
                int value1 = sc.nextInt();
                ll.insertAtEnd(value1);
                System.out.println("The value inserted at the end.");
                break;
                case 3:
                System.out.print("Enter the value: ");
                int value2 = sc.nextInt();
                ll.insertAtStart(value2);
                System.out.println("The value inserted at the start");
                break;
                case 4:
                System.out.print("Enter the position: ");
                int position1 = sc.nextInt();
                System.out.print("Enter the value: ");
                int value3 = sc.nextInt();
                ll.insertAtAnyposition(position1, value3);
                System.out.println("The value inserted in the " + position1 + "th position.");
                break;
                case 5:
                System.out.print("The linked list is: ");
                ll.display();
                System.out.println();
                break;
                case 6:
                ll.reverse();
                System.out.print("Linked list reversed.");
                break;
                case 7:
                System.out.print("Enter the index: ");
                int index1 = sc.nextInt();
                System.out.println("Element at the " + index1 + "th index is: " + ll.getvalue(index1));
                break;
                case 8:
                System.out.print("Enter the index: ");
                int index2 = sc.nextInt();
                System.out.print("Enter the new value: ");
                int value4 = sc.nextInt();
                ll.setvalue(index2, value4);
                System.out.println("New value " + value4 + " is set at the index " + index2);
                break;
                case 9:
                ll.deleteAtEnd();
                System.out.println("Last element deleted.");
                break;
                case 10:
                ll.deleteAtStart();
                System.out.println("First element deleted.");
                break;
                case 11:
                System.out.print("Enter the position of node to delete: ");
                int position2 = sc.nextInt();
                ll.deleteAtAnyposition(position2);
                System.out.println("Element deleted from " + position2 + "th position");
                break;
                case 12:
                System.out.println("Program exited.");
                System.out.println("Final size: " + ll.size);
                break;
                default:
                System.out.println("Invalid choice");
                break;
                }
            } while (ch != 12);
            System.out.println();
        }
}