Clone a Linked List with next and Random Pointer

Last Updated : 22 Sep, 2023

Given a linked list of size N where each node has two links: one pointer points to the next node and the second pointer points to any node in the list. The task is to create a clone of this linked list in O(N) time.

Note: The pointer pointing to the next node is ‘next‘ pointer and the one pointing to an arbitrary node is called ‘arbit’ pointer as it can point to any arbitrary node in the linked list.

An example of the linked list is shown in the below image:

An example of linked list with a random pointerAn example of linked list with a random pointer

Clone a Linked List with next and Random Pointer using Extra Space:

First create a single linked list with only the ‘next’ pointer and use a mapping to map the new nodes to their corresponding nodes in the given linked list. Now use this mapping to point the arbitrary node from any node in the newly created list.

Follow the steps mentioned below to implement the above idea:

Create a duplicate (say Y) for each node (say X) and map them with corresponding old nodes (say mp, So mp[X] = Y).
Create the single linked list of the duplicate nodes where each node only has the ‘next’ pointer.
Now iterate over the old linked list and do the following:
- Find the duplicate node mapped with the current one. (i.e., if the current node is X then duplicate is mp[x])
- Make the arbit pointer of the duplicate node pointing to the duplicate of the current->arbit node (i.e., mp[x]->arbit will point to mp[X->arbit]).
The linked list created in this way is the required linked list.

Follow the illustration below for a better understanding:

Illustration:

Consider the linked list shown below:

Original linked list

The green links are the arbit pointers

Creating copy of Nodes and next pointer:

Initially create single linked list of duplicate nodes with only the next pointers and map them with the old ones.
Here the blue coloured links are used to show the mapping.

New linked list mapped with old nodes

Linking the arbit pointers:

Now iterating the old array and update the arbit pointers as mentioned in the approach. The green coloured links are the arbit pointers.

At first node:

Linking arbit pointer of duplicate of 1st node

At second node:

Linking arbit pointer of duplicate of 2nd node

At third node:

Linking arbit pointer of duplicate of 3rd node

At fourth node:

Linking arbit pointer of duplicate of 4th node

At fifth node:

Linking arbit pointer of duplicate of 5th node

The final linked list is as shown below:

The original and the clone

Below is the implementation of the above approach:

C++14

// C++ code to implement the approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Structure of a node of linked list
struct Node {
    int val;
    Node* next;
    Node* arbit;
   
    // Constructor
    Node(int x)
    {
        this->val = x;
        this->next = NULL;
        this->arbit = NULL;
    }
};
 
// Function to clone the linked list
Node* cloneLinkedList(Node* head)
{
    // Map to store the mapping of 
    // old nodes with new ones
    unordered_map<Node*, Node*> mp;
    Node *temp, *nhead;
   
    // Duplicate of the first node
    temp = head;
    nhead = new Node(temp->val);
    mp[temp] = nhead;
   
    // Loop to create duplicates of nodes 
    // with only next pointer
    while (temp->next != NULL) {
        nhead->next 
            = new Node(temp->next->val);
        temp = temp->next;
        nhead = nhead->next;
        mp[temp] = nhead;
    }
    temp = head;
   
    // Loop to clone the arbit pointers
    while (temp != NULL) {
        mp[temp]->arbit = mp[temp->arbit];
        temp = temp->next;
    }
   
    // Return the head of the clone
    return mp[head];
}
 
// Function to print the linked list
void printList(Node* head)
{
    cout << head->val << "("
         << head->arbit->val << ")";
    head = head->next;
    while (head != NULL) {
        cout << " -> " << head->val << "("
             << head->arbit->val << ")";
        head = head->next;
    }
    cout << endl;
}
 
// Driver code
int main()
{
    // Creating a linked list with random pointer
    Node* head = new Node(1);
    head->next = new Node(2);
    head->next->next = new Node(3);
    head->next->next->next = new Node(4);
    head->next->next->next->next 
        = new Node(5);
    head->arbit = head->next->next;
    head->next->arbit = head;
    head->next->next->arbit 
        = head->next->next->next->next;
    head->next->next->next->arbit 
        = head->next->next;
    head->next->next->next->next->arbit 
        = head->next;
   
    // Print the original list
    cout << "The original linked list:\n";
    printList(head);
   
    // Function call
    Node* sol = cloneLinkedList(head);
   
    cout << "The cloned linked list:\n";
    printList(sol);
   
    return 0;
}

Java

// Java code to implement the approach
 
import java.io.*;
import java.util.HashMap;
 
class Node {
  int val;
  Node next;
  Node arbit;
 
  // Constructor
  Node(int x)
  {
    this.val = x;
    this.next = null;
    this.arbit = null;
  }
}
 
class GFG {
 
  static Node cloneLinkedList(Node head)
  {
    // Map to store the mapping of
    // old nodes with new ones
    HashMap<Node, Node> mp = new HashMap<>();
    Node temp, nhead;
 
    // Duplicate of the first node
    temp = head;
    nhead = new Node(temp.val);
    mp.put(temp, nhead);
 
    // Loop to create duplicates of nodes
    // with only next pointer
    while (temp.next != null) {
      nhead.next = new Node(temp.next.val);
      temp = temp.next;
      nhead = nhead.next;
      mp.put(temp, nhead);
    }
    temp = head;
 
    // Loop to clone the arbit pointers
    while (temp != null) {
      mp.get(temp).arbit = mp.get(temp.arbit);
      temp = temp.next;
    }
 
    // Return the head of the clone
    return mp.get(head);
  }
 
  static void printList(Node head)
  {
    System.out.print(head.val + "(" + head.arbit.val
                     + ")");
    head = head.next;
    while (head != null) {
      System.out.print(" -> " + head.val + "("
                       + head.arbit.val + ")");
      head = head.next;
    }
    System.out.println();
  }
 
  public static void main(String[] args)
  {
    // Creating a linked list with random pointer
    Node head = new Node(1);
    head.next = new Node(2);
    head.next.next = new Node(3);
    head.next.next.next = new Node(4);
    head.next.next.next.next = new Node(5);
    head.arbit = head.next.next;
    head.next.arbit = head;
    head.next.next.arbit = head.next.next.next.next;
    head.next.next.next.arbit = head.next.next;
    head.next.next.next.next.arbit = head.next;
 
    // Print the original list
    System.out.println("The original linked list:");
    printList(head);
 
    // Function call
    Node sol = cloneLinkedList(head);
 
    System.out.println("The cloned linked list:");
    printList(sol);
  }
}
 
/// This code is contributed by lokesh.

Python3

# Structure of a node of linked list
class Node:
    def __init__(self, val):
        self.val = val
        self.next = None
        self.arbit = None
 
# Function to clone the linked list
def cloneLinkedList(head):
    # Map to store the mapping of
    # old nodes with new ones
    mp = {}
    temp = head
    nhead = Node(temp.val)
    mp[temp] = nhead
 
    # Loop to create duplicates of nodes
    # with only next pointer
    while temp.next:
        nhead.next = Node(temp.next.val)
        temp = temp.next
        nhead = nhead.next
        mp[temp] = nhead
 
    temp = head
 
    # Loop to clone the arbit pointers
    while temp:
        mp[temp].arbit = mp[temp.arbit]
        temp = temp.next
 
    # Return the head of the clone
    return mp[head]
 
# Function to print the linked list
def printList(head):
    result = []
    while head:
        result.append(f"{head.val}({head.arbit.val})")
        head = head.next
    print(" -> ".join(result))
 
# Creating a linked list with random pointer
head = Node(1)
head.next = Node(2)
head.next.next = Node(3)
head.next.next.next = Node(4)
head.next.next.next.next = Node(5)
head.arbit = head.next.next
head.next.arbit = head
head.next.next.arbit = head.next.next.next.next
head.next.next.next.arbit = head.next.next
head.next.next.next.next.arbit = head.next
 
# Print the original list
print("The original linked list:")
printList(head)
 
# Function call
sol = cloneLinkedList(head)
 
print("The cloned linked list:")
printList(sol)

C#

// C# code to implement the approach
using System;
using System.Collections.Generic;
 
class Node {
    public int val;
    public Node next;
    public Node arbit;
 
    // Constructor
    public Node(int x)
    {
        this.val = x;
        this.next = null;
        this.arbit = null;
    }
}
 
public class GFG {
 
    static Node cloneLinkedList(Node head)
    {
        // Map to store the mapping of
        // old nodes with new ones
        Dictionary<Node, Node> mp
            = new Dictionary<Node, Node>();
        Node temp, nhead;
 
        // Duplicate of the first node
        temp = head;
        nhead = new Node(temp.val);
        mp[temp] = nhead;
 
        // Loop to create duplicates of nodes
        // with only next pointer
        while (temp.next != null) {
            nhead.next = new Node(temp.next.val);
            temp = temp.next;
            nhead = nhead.next;
            mp[temp] = nhead;
        }
        temp = head;
 
        // Loop to clone the arbit pointers
        while (temp != null) {
            mp[temp].arbit = mp[temp.arbit];
            temp = temp.next;
        }
 
        // Return the head of the clone
        return mp[head];
    }
 
    static void printList(Node head)
    {
        Console.Write(head.val + "(" + head.arbit.val
                      + ")");
        head = head.next;
        while (head != null) {
            Console.Write(" -> " + head.val + "("
                          + head.arbit.val + ")");
            head = head.next;
        }
        Console.WriteLine();
    }
 
    static public void Main()
    {
 
        // Code
        // Creating a linked list with random pointer
        Node head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(4);
        head.next.next.next.next = new Node(5);
        head.arbit = head.next.next;
        head.next.arbit = head;
        head.next.next.arbit = head.next.next.next.next;
        head.next.next.next.arbit = head.next.next;
        head.next.next.next.next.arbit = head.next;
 
        // Print the original list
        Console.WriteLine("The original linked list:");
        printList(head);
 
        // Function call
        Node sol = cloneLinkedList(head);
 
        Console.WriteLine("The cloned linked list:");
        printList(sol);
    }
}
 
// This code is contributed by lokeshmvs21.

Javascript

// Javascript code to implement the approach
class Node {
  constructor(val) {
    this.val = val;
    this.next = null;
    this.arbit = null;
  }
}
 
const cloneLinkedList = (head) => {
 
  // Map to store the mapping of old nodes with new ones
  const mp = new Map();
  let temp = head;
  let nhead = new Node(temp.val);
  mp.set(temp, nhead);
 
  // Loop to create duplicates of nodes with only next pointer
  while (temp.next) {
    nhead.next = new Node(temp.next.val);
    temp = temp.next;
    nhead = nhead.next;
    mp.set(temp, nhead);
  }
  temp = head;
 
  // Loop to clone the arbit pointers
  while (temp) {
    mp.get(temp).arbit = mp.get(temp.arbit);
    temp = temp.next;
  }
 
  // Return the head of the clone
  return mp.get(head);
}
 
const printList = (head) => {
  let str = `${head.val}(${head.arbit.val})`;
  head = head.next;
  while (head) {
    str += ` -> ${head.val}(${head.arbit.val})`;
    head = head.next;
  }
  console.log(str);
}
 
// Creating a linked list with random pointer
const head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(4);
head.next.next.next.next = new Node(5);
head.arbit = head.next.next;
head.next.arbit = head;
head.next.next.arbit = head.next.next.next.next;
head.next.next.next.arbit = head.next.next;
head.next.next.next.next.arbit = head.next;
 
// Print the original list
console.log("The original linked list:");
printList(head);
 
// Function call
const sol = cloneLinkedList(head);
 
console.log("The cloned linked list:");
printList(sol);
 
// This code is contributed by shivamsharma215

Output

The original linked list:
1(3) -> 2(1) -> 3(5) -> 4(3) -> 5(2)
The cloned linked list:
1(3) -> 2(1) -> 3(5) -> 4(3) -> 5(2)

Time Complexity: O(N)
Auxiliary Space: O(N)

Clone a Linked List with next and Random Pointer without using any Extra Space:

Create duplicate of a node and insert it in between that node and the node just next to it.

Now for a node X its duplicate will be X->next and the arbitrary pointer of the duplicate will point to X->arbit->next [as that is the duplicate of X->arbit]

Follow the steps mentioned below to implement the idea:

Create the copy of node 1 and insert it between node 1 and node 2 in the original Linked List, create the copy of node 2 and insert it between 2^nd and 3^rd node and so on. Add the copy of N after the Nth node
Now copy the arbitrary link in this fashion:

original->next->arbitrary = original->arbitrary->next

Now restore the original and copy linked lists in this fashion in a single loop.

original->next = original->next->next;
copy->next = copy->next->next;

Make sure that the last element of original->next is NULL.

C++

// C++ code to implement the approach
 
#include <bits/stdc++.h>
using namespace std;
 
 
 
struct Node {
    int data;
    Node *next, *random;
    Node(int x) {
        data = x;
        next = random = NULL;
    }
};
 
Node* cloneLinkedList(Node* head) {
    if (head == NULL) {
        return NULL;
    }
     
    // Step 1: Create new nodes and insert them next to the original nodes
    Node* curr = head;
    while (curr != NULL) {
        Node* newNode = new Node(curr->data);
        newNode->next = curr->next;
        curr->next = newNode;
        curr = newNode->next;
    }
     
    // Step 2: Set the random pointers of the new nodes
    curr = head;
    while (curr != NULL) {
        if (curr->random != NULL) {
            curr->next->random = curr->random->next;
        }
        curr = curr->next->next;
    }
     
    // Step 3: Separate the new nodes from the original nodes
    curr = head;
    Node* clonedHead = head->next;
    Node* clonedCurr = clonedHead;
    while (clonedCurr->next != NULL) {
        curr->next = curr->next->next;
        clonedCurr->next = clonedCurr->next->next;
        curr = curr->next;
        clonedCurr = clonedCurr->next;
    }
    curr->next = NULL;
    clonedCurr->next = NULL;
     
    return clonedHead;
}
 
 
// Function to print the linked list
void printList(Node* head)
{
    cout << head->data << "("
        << head->random->data << ")";
    head = head->next;
    while (head != NULL) {
        cout << " -> " << head->data << "("
            << head->random->data << ")";
        head = head->next;
    }
    cout << endl;
}
 
// Driver code
int main()
{
    // Creating a linked list with random pointer
    Node* head = new Node(1);
    head->next = new Node(2);
    head->next->next = new Node(3);
    head->next->next->next = new Node(4);
    head->next->next->next->next
        = new Node(5);
    head->random = head->next->next;
    head->next->random = head;
    head->next->next->random
        = head->next->next->next->next;
    head->next->next->next->random
        = head->next->next;
    head->next->next->next->next->random
        = head->next;
     
    // Print the original list
    cout << "The original linked list:\n";
    printList(head);
     
    // Function call
    Node* sol = cloneLinkedList(head);
     
    cout << "The cloned linked list:\n";
    printList(sol);
     
    return 0;
}

Java

class Node {
    int data;
    Node next, random;
 
    Node(int x) {
        data = x;
        next = random = null;
    }
}
 
public class Main {
    public static void main(String[] args) {
        // Creating a linked list with random pointer
        Node head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(4);
        head.next.next.next.next = new Node(5);
        head.random = head.next.next;
        head.next.random = head;
        head.next.next.random = head.next.next.next.next;
        head.next.next.next.random = head.next.next;
        head.next.next.next.next.random = head.next;
 
        // Print the original list
        System.out.println("The original linked list:");
        printList(head);
 
        // Function call
        Node sol = cloneLinkedList(head);
 
        System.out.println("The cloned linked list:");
        printList(sol);
    }
 
    public static Node cloneLinkedList(Node head) {
        if (head == null) {
            return null;
        }
 
        // Step 1: Create new nodes and insert them next to the original nodes
        Node curr = head;
        while (curr != null) {
            Node newNode = new Node(curr.data);
            newNode.next = curr.next;
            curr.next = newNode;
            curr = newNode.next;
        }
 
        // Step 2: Set the random pointers of the new nodes
        curr = head;
        while (curr != null) {
            if (curr.random != null) {
                curr.next.random = curr.random.next;
            }
            curr = curr.next.next;
        }
 
        // Step 3: Separate the new nodes from the original nodes
        curr = head;
        Node clonedHead = head.next;
        Node clonedCurr = clonedHead;
        while (clonedCurr.next != null) {
            curr.next = curr.next.next;
            clonedCurr.next = clonedCurr.next.next;
            curr = curr.next;
            clonedCurr = clonedCurr.next;
        }
        curr.next = null;
        clonedCurr.next = null;
 
        return clonedHead;
    }
 
    // Function to print the linked list
    public static void printList(Node head) {
        System.out.print(head.data + "(" + head.random.data + ")");
        head = head.next;
        while (head != null) {
            System.out.print(" -> " + head.data + "(" + head.random.data + ")");
            head = head.next;
        }
        System.out.println();
    }
}

Python3

class Node:
    def __init__(self, x):
        self.data = x
        self.next = None
        self.random = None
 
 
def cloneLinkedList(head):
    if head == None:
        return None
    # Step 1: Create new nodes and insert them next to the original nodes
    curr = head
    while curr != None:
        newNode = Node(curr.data)
        newNode.next = curr.next
        curr.next = newNode
        curr = newNode.next
    # Step 2: Set the random pointers of the new nodes
    curr = head
    while curr != None:
        if curr.random != None:
            curr.next.random = curr.random.next
        curr = curr.next.next
    # Step 3: Separate the new nodes from the original nodes
    curr = head
    clonedHead = head.next
    clonedCurr = clonedHead
    while clonedCurr.next != None:
        curr.next = curr.next.next
        clonedCurr.next = clonedCurr.next.next
        curr = curr.next
        clonedCurr = clonedCurr.next
    curr.next = None
    clonedCurr.next = None
    return clonedHead
 
# Function to print the linked list
 
 
def printList(head):
    print(head.data, "(", head.random.data, ")", end="")
    head = head.next
    while head != None:
        print("->", head.data, "(", head.random.data, ")", end="")
        head = head.next
    print()
 
 
# Driver code
if __name__ == '__main__':
    # Creating a linked list with random pointer
    head = Node(1)
    head.next = Node(2)
    head.next.next = Node(3)
    head.next.next.next = Node(4)
    head.next.next.next.next = Node(5)
    head.random = head.next.next
    head.next.random = head
    head.next.next.random = head.next.next.next.next
    head.next.next.next.random = head.next.next
    head.next.next.next.next.random = head.next
 
    # Print the original list
    print("The original linked list:")
    printList(head)
 
    # Function call
    sol = cloneLinkedList(head)
    print("The cloned linked list:")
    printList(sol)

C#

using System;
 
public class Node {
    public int data;
    public Node next, random;
 
    public Node(int x) {
        data = x;
        next = random = null;
    }
}
 
public class GFG {
 
    public static Node CloneLinkedList(Node head) {
        if (head == null) {
            return null;
        }
 
        // Step 1: Create new nodes and insert them next to the original nodes
        Node curr = head;
        while (curr != null) {
            Node newNode = new Node(curr.data);
            newNode.next = curr.next;
            curr.next = newNode;
            curr = newNode.next;
        }
 
        // Step 2: Set the random pointers of the new nodes
        curr = head;
        while (curr != null) {
            if (curr.random != null) {
                curr.next.random = curr.random.next;
            }
            curr = curr.next.next;
        }
 
        // Step 3: Separate the new nodes from the original nodes
        curr = head;
        Node clonedHead = head.next;
        Node clonedCurr = clonedHead;
        while (clonedCurr.next != null) {
            curr.next = curr.next.next;
            clonedCurr.next = clonedCurr.next.next;
            curr = curr.next;
            clonedCurr = clonedCurr.next;
        }
        curr.next = null;
        clonedCurr.next = null;
 
        return clonedHead;
    }
 
    // Function to print the linked list
    public static void PrintList(Node head) {
        Console.Write(head.data + "(" + head.random.data + ")");
        head = head.next;
        while (head != null) {
            Console.Write(" -> " + head.data + "(" + head.random.data + ")");
            head = head.next;
        }
        Console.WriteLine();
    }
      public static void Main() {
        // Creating a linked list with random pointer
        Node head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(4);
        head.next.next.next.next = new Node(5);
        head.random = head.next.next;
        head.next.random = head;
        head.next.next.random = head.next.next.next.next;
        head.next.next.next.random = head.next.next;
        head.next.next.next.next.random = head.next;
 
        // Print the original list
        Console.WriteLine("The original linked list:");
        PrintList(head);
 
        // Function call
        Node sol = CloneLinkedList(head);
 
        Console.WriteLine("The cloned linked list:");
        PrintList(sol);
    }
 
}

Javascript

// JavaScript code to implement the approach
 
class Node {
  constructor(x) {
    this.data = x;
    this.next = null;
    this.random = null;
  }
}
 
function cloneLinkedList(head) {
  if (head === null) {
    return null;
  }
 
  // Step 1: Create new nodes and insert them next to the original nodes
  let curr = head;
  while (curr !== null) {
    const newNode = new Node(curr.data);
    newNode.next = curr.next;
    curr.next = newNode;
    curr = newNode.next;
  }
 
  // Step 2: Set the random pointers of the new nodes
  curr = head;
  while (curr !== null) {
    if (curr.random !== null) {
      curr.next.random = curr.random.next;
    }
    curr = curr.next.next;
  }
 
  // Step 3: Separate the new nodes from the original nodes
  curr = head;
  const clonedHead = head.next;
  let clonedCurr = clonedHead;
  while (clonedCurr.next !== null) {
    curr.next = curr.next.next;
    clonedCurr.next = clonedCurr.next.next;
    curr = curr.next;
    clonedCurr = clonedCurr.next;
  }
  curr.next = null;
  clonedCurr.next = null;
 
  return clonedHead;
}
 
// Function to print the linked list
function printList(head) {
  process.stdout.write(head.data + "(" + (head.random.data + ")"));
  head = head.next;
  while (head !== null) {
    process.stdout.write(" -> " + head.data + "(" + (head.random.data + ")"));
    head = head.next;
  }
  console.log();
}
 
// Driver code
// Creating a linked list with random pointer
const head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(4);
head.next.next.next.next = new Node(5);
head.random = head.next.next;
head.next.random = head;
head.next.next.random = head.next.next.next.next;
head.next.next.next.random = head.next.next;
head.next.next.next.next.random = head.next;
 
// Print the original list
console.log("The original linked list:");
printList(head);
 
// Function call
const sol = cloneLinkedList(head);
 
console.log("The cloned linked list:");
printList(sol);
 
// The code is contributed by Arushi Goel.

Output

The original linked list:
1(3) -> 2(1) -> 3(5) -> 4(3) -> 5(2)
The cloned linked list:
1(3) -> 2(1) -> 3(5) -> 4(3) -> 5(2)

Time Complexity: O(N)
Auxiliary Space: O(1)

Suggest improvement

The Great Tree-List Recursion Problem.

Convert given Binary Tree to Doubly Linked List in Linear time

Share your thoughts in the comments

Types of Linked List

Basic operations on Linked List

Easy problems on Linked List

Medium problems on Linked List

Hard problems on Linked List

Types of Linked List

Basic operations on Linked List

Easy problems on Linked List

Medium problems on Linked List

Hard problems on Linked List

Clone a Linked List with next and Random Pointer

Clone a Linked List with next and Random Pointer using Extra Space:

C++14

Java

Python3

C#

Javascript

Clone a Linked List with next and Random Pointer without using any Extra Space:

C++

Java

Python3

C#

Javascript

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