DSA/algorithms/Java/linked-lists/clone-linkedlist.java

// Java program to clone a linked list with random pointers
import java.util.HashMap;
import java.util.Map;
  
// Linked List Node class
class Node
{
    int data;//Node data
    Node next, random;//Next and random reference
  
    //Node constructor
    public Node(int data)
    {
        this.data = data;
        this.next = this.random = null;
    }
}
  
// linked list class
class LinkedList
{
    Node head;//Linked list head reference
  
    // Linked list constructor
    public LinkedList(Node head)
    {
        this.head = head;
    }
  
    // push method to put data always at the head
    // in the linked list.
    public void push(int data)
    {
        Node node = new Node(data);
        node.next = this.head;
        this.head = node;
    }
  
    // Method to print the list.
    void print()
    {
        Node temp = head;
        while (temp != null)
        {
            Node random = temp.random;
            int randomData = (random != null)? random.data: -1;
            System.out.println("Data = " + temp.data +
                               ", Random data = "+ randomData);
            temp = temp.next;
        }
    }
  
    // Actual clone method which returns head
    // reference of cloned linked list.
    public LinkedList clone()
    {
        // Initialize two references, one with original
        // list's head.
        Node origCurr = this.head, cloneCurr = null;
  
        // Hash map which contains node to node mapping of
        // original and clone linked list.
        Map<Node, Node> map = new HashMap<Node, Node>();
  
        // Traverse the original list and make a copy of that
        // in the clone linked list.
        while (origCurr != null)
        {
            cloneCurr = new Node(origCurr.data);
            map.put(origCurr, cloneCurr);
            origCurr = origCurr.next;
        }
  
        // Adjusting the original list reference again.
        origCurr = this.head;
  
        // Traversal of original list again to adjust the next
        // and random references of clone list using hash map.
        while (origCurr != null)
        {
            cloneCurr = map.get(origCurr);
            cloneCurr.next = map.get(origCurr.next);
            cloneCurr.random = map.get(origCurr.random);
            origCurr = origCurr.next;
        }
  
        //return the head reference of the clone list.
        return new LinkedList(map.get(this.head));
    }
}
  
// Driver Class
class Main
{
    // Main method.
    public static void main(String[] args)
    {
        // Pushing data in the linked list.
        LinkedList list = new LinkedList(new Node(5));
        list.push(4);
        list.push(3);
        list.push(2);
        list.push(1);
  
        // Setting up random references.
        list.head.random = list.head.next.next;
        list.head.next.random =
            list.head.next.next.next;
        list.head.next.next.random =
            list.head.next.next.next.next;
        list.head.next.next.next.random =
            list.head.next.next.next.next.next;
        list.head.next.next.next.next.random =
            list.head.next;
  
        // Making a clone of the original linked list.
        LinkedList clone = list.clone();
  
        // Print the original and cloned linked list.
        System.out.println("Original linked list");
        list.print();
        System.out.println("\nCloned linked list");
        clone.print();
    }
}