Java Program to Insert a New Node at the Middle of the Circular Linked List

Given a Circular Linked List, the task is to add a New Node at the Middle of the List. Let’s consider the following Circular Linked List:

List-Before-Insertion

List-After-Insertion

1. Create a new node (New_node).
2. Check for an empty list. If the list is empty then insert the node as head.
3. For non-empty list, calculate the length of the list. 
4. Create variable mid and store middle length in it.
5. Create two nodes Temporary and Current.  
6. Now traverse the list till Temporary reaches the midpoint of the list using the mid variable.
7. Insert the New_node after the Current.
8. Make Current.next point to New node and New_node.next to Temporary.
9. Node is inserted.

Below is the implementation of the above approach:

Java

// Java Program to Insert a New Node at
// the Middle of the Circular Linked List
import java.io.*;

public class GFG {
    // Stores Information about Node of List
    public class Node {
        int data;
        Node next;
        public Node(int data) { this.data = data; }
    }

    // Declaring Head of the Node
    public Node head_of_node = null;

    // A last pointer to help append values to our list
    public Node last = null;

    // keep count of  size of the list
    public int length_of_list;

    // Add method adds values to the end of the list
    public void add(int data)
    {
        Node newNode = new Node(data);
        if (head_of_node == null) {
            head_of_node = newNode;
            last = newNode;
            newNode.next = head_of_node;
        }
        else {
            last.next = newNode;
            last = newNode;
            last.next = head_of_node;
        }
        // keep count of size of list
        length_of_list++;
    }

    // Method to insert Node in the middle of the list
    public void Insert_In_Middle(int data)
    {

        // creating a new node that is to be inserted
        Node New_node = new Node(data);

        // check for empty list
        if (head_of_node == null) {
            head_of_node = New_node;
            last = New_node;
            New_node.next = head_of_node;
        }

        // If the list is not empty
        else {
            // Declaring nodes
            Node temporary;
            Node current;

            // Checking if the length of list
            // if even or odd

            int mid_point_check = (length_of_list % 2);

            // mid point for even length
            if (mid_point_check == 0) {
                length_of_list = length_of_list / 2;
            }
            // mid point for odd length
            else {
                length_of_list = (length_of_list + 1) / 2;
            }

            // temporary points to the head of list
            temporary = head_of_node;
            current = null;
            // loop till we reach the mid point
            while (length_of_list > 0) {

                // make current point to the previous node
                current = temporary;
                temporary = temporary.next;
                length_of_list -= 1;
            }

            // make the previous node point to the new node
            current.next = New_node;

            //  make the new_node.next point to temporary
            New_node.next = temporary;
        }
        // increasing the length of list after insertion of
        // new node
        length_of_list++;
    }

    // Print_list method iterates through the list and
    // prints the values stored in the list
    public void Print_List()
    {
        Node current = head_of_node;
        if (head_of_node == null) {
            System.out.println("Your list is empty");
        }
        else {
            do {
                System.out.print(" " + current.data);
                current = current.next;
            } while (current != head_of_node);
            System.out.println();
        }
    }

    // Driver code
    public static void main(String[] args)
    {

        GFG circular_list = new GFG();
        circular_list.add(10);
        circular_list.add(20);
        circular_list.add(30);
        circular_list.add(40);

        System.out.print("Original List        --> ");
        circular_list.Print_List();
        circular_list.Insert_In_Middle(60);
        System.out.print("List after Inserting --> ");
        circular_list.Print_List();
    }
}

Output

Original List        -->  10 20 30 40
List after Inserting -->  10 20 60 30 40

Time complexity: O(n) where n is no of nodes of circular linked list

Auxiliary space: O(1) because using constant variables