Clone a linked list with next and random pointer | Set 2

3.4

We have already discussed 2 different ways to clone a linked list. In this post, one more simple method to clone a linked list is discussed.

The idea is to use Hashing. Below is algorithm.
1. Traverse the original linked list and make a copy in terms of data.
2. Make a hash map of key value pair with original linked list node and copied linked list node.
3. Traverse the original linked list again and using the hash map adjust the next and random reference of cloned linked list nodes.

Below is the implementation of above approach.

C++

// C++ program to clone a linked list with
// random pointers
#include<bits/stdc++.h>
using namespace std;


// Linked List Node
class Node
{
    public:
    int data;//Node data
    
    // Next and random reference
    Node *next, *random;

    Node(int data)
    {
        this->data = data;
        this->next = this->random = NULL;
    }
};

// linked list class
class LinkedList
{
    public:
    Node *head;// Linked list head reference

    LinkedList(Node *head)
    {
        this->head = head;
    }

    // push method to put data always at
    // the head in the linked list.
    void push(int data)
    {
        Node *node = new Node(data);
        node->next = head;
        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;
            cout << "Data = " << temp->data 
                 << ", ";
            cout << "Random Data = " << 
                 randomData << endl;
            temp = temp->next;
        }
        cout << endl;
    }

    // Actual clone method which returns
    // head reference of cloned linked
    // list.
    LinkedList* clone()
    {
        // Initialize two references,
        // one with original list's head.
        Node *origCurr = head;
        Node *cloneCurr = NULL;

        // Hash map which contains node 
        // to node mapping of original 
        // and clone linked list.
        unordered_map<Node*, Node*> mymap;

        // Traverse the original list and
        // make a copy of that in the 
        // clone linked list.
        while (origCurr != NULL)
        {
            cloneCurr = new Node(origCurr->data);
            mymap[origCurr] = cloneCurr;
            origCurr = origCurr->next;
        }

        // Adjusting the original list 
        // reference again.
        origCurr = head;

        // Traversal of original list again
        // to adjust the next and random 
        // references of clone list using 
        // hash map.
        while (origCurr != NULL)
        {
            cloneCurr = mymap[origCurr];
            cloneCurr->next = mymap[origCurr->next];
            cloneCurr->random = mymap[origCurr->random];
            origCurr = origCurr->next;
        }

        // return the head reference of 
        // the clone list.
        return new LinkedList(mymap[head]);
    }
};

// driver code
int main()
{
    // Pushing data in the linked list.
    LinkedList *mylist = new LinkedList(new Node(5));
    mylist->push(4);
    mylist->push(3);
    mylist->push(2);
    mylist->push(1);

    // Setting up random references.
    mylist->head->random = mylist->head->next->next;

    mylist->head->next->random =
        mylist->head->next->next->next;

    mylist->head->next->next->random =
        mylist->head->next->next->next->next;

    mylist->head->next->next->next->random =
        mylist->head->next->next->next->next->next;

    mylist->head->next->next->next->next->random =
        mylist->head->next;

    // Making a clone of the original
    // linked list.
    LinkedList *clone = mylist->clone();

    // Print the original and cloned 
    // linked list.
    cout << "Original linked list\n";
    mylist->print();
    cout << "\nCloned linked list\n";
    clone->print();
}
// This code is contributed by Chhavi

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();
    }
}


Output:
Original linked list
Data = 1, Random data = 3
Data = 2, Random data = 4
Data = 3, Random data = 5
Data = 4, Random data = -1
Data = 5, Random data = 2

Cloned linked list
Data = 1, Random data = 3
Data = 2, Random data = 4
Data = 3, Random data = 5
Data = 4, Random data = -1
Data = 5, Random data = 2

Time complexity : O(n)
Auxiliary space : O(n)

This article is contributed by Kumar Gautam. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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