// Java program to merge a linked list 
// into another at alternate positions
public class LinkedList
{
    // head of list
    Node head;  

    // Linked list Node
    class Node
    {
        int data;
        Node next;
        Node(int d) 
        {
            data = d; 
            next = null; 
        }
    }

    /* Inserts a new Node at front 
       of the list. */
    void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);

        // 3. Make next of new Node as head 
        new_node.next = head;

        /* 4. Move the head to point to new 
              Node */
        head = new_node;
    }

    // Main function that inserts nodes of 
    // linked list q into p at alternate positions. 
    // Since head of first list never changes and 
    // head of second list/ may change, we need single
    // pointer for first list and double pointer for 
    // second list.
    void merge(LinkedList q)
    {
        Node p_curr = head, 
             q_curr = q.head;
        Node p_next, q_next;

        // While there are available positions 
        // in p;
        while (p_curr != null && 
               q_curr != null) 
        {
            // Save next pointers
            p_next = p_curr.next;
            q_next = q_curr.next;

            // make q_curr as next of p_curr
            // change next pointer of q_curr
            q_curr.next = p_next; 

            // change next pointer of p_curr
            p_curr.next = q_curr; 

            // update current pointers for 
            // next iteration
            p_curr = p_next;
            q_curr = q_next;
        }
        q.head = q_curr;
    }

    // Function to print linked list 
    void printList()
    {
        Node temp = head;
        while (temp != null)
        {
           System.out.print(temp.data + " ");
           temp = temp.next;
        }
        System.out.println();
    }

    // Driver code
    public static void main(String args[])
    {
        LinkedList llist1 = 
        new LinkedList();
        LinkedList llist2 = 
        new LinkedList();
        llist1.push(3);
        llist1.push(2);
        llist1.push(1);

        System.out.println(
               "First Linked List:");
        llist1.printList();

        llist2.push(8);
        llist2.push(7);
        llist2.push(6);
        llist2.push(5);
        llist2.push(4);

        System.out.println(
               "Second Linked List:");

        llist1.merge(llist2);

        System.out.println(
               "Modified first linked list:");
        llist1.printList();

        System.out.println(
               "Modified second linked list:");
        llist2.printList();
    }
} 
// This code is contributed by Rajat Mishra