Java Program To Check If Two Linked Lists Are Identical

// An iterative Java program to check if two 
// linked lists are identical or not
class LinkedList
{
    // Head of list
    Node head;  

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

    /* Returns true if linked lists a and b 
       are identical, otherwise false */
    boolean areIdentical(LinkedList listb)
    {
        Node a = this.head, b = listb.head;
        while (a != null && b != null)
        {
            if (a.data != b.data)
                return false;

            /* If we reach here, then a and b 
               are not null and their data is 
               same, so move to next nodes in 
               both lists */
            a = a.next;
            b = b.next;
        }

        // If linked lists are identical, then 
        // 'a' and 'b' must be null at this point.
        return (a == null && b == null);
    }

    // UTILITY FUNCTIONS TO TEST fun1() and fun2() 
    /*  Given a reference (pointer to pointer) to 
        the head of a list and an int, push a new 
        node on the 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;
    }

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

        /* The constructed linked lists are :
           llist1: 3->2->1
           llist2: 3->2->1 */
        llist1.push(1);
        llist1.push(2);
        llist1.push(3);

        llist2.push(1);
        llist2.push(2);
        llist2.push(3);

        if (llist1.areIdentical(llist2) == true)
            System.out.println("Identical ");
        else
            System.out.println("Not identical ");

    }
} 
// This code is contributed by Rajat Mishra 

// A recursive Java method to check if two 
// linked lists are identical or not
boolean areIdenticalRecur(Node a, Node b)
{
    // If both lists are empty
    if (a == null && b == null)
        return true;

    // If both lists are not empty, then 
    // data of current nodes must match, 
    // and same should be recursively true 
    // for rest of the nodes.
    if (a != null && b != null)
        return (a.data == b.data) &&
               areIdenticalRecur(a.next, b.next);

    // If we reach here, then one of the lists
    // is empty and other is not
    return false;
}

/* Returns true if linked lists a and b 
   are identical, otherwise false */
boolean areIdentical(LinkedList listb)
{
    return areIdenticalRecur(this.head, 
                             listb.head);
}