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# Clone a linked list with next and random pointer in O(1) space

Given a linked list having two pointers in each node. The first one points to the next node of the list, however, the other pointer is random and can point to any node of the list. Write a program that clones the given list in O(1) space, i.e., without any extra space.

Examples:

Output :
A new linked list identical to the original list.

In the previous posts Set-1 and Set-2 various methods are discussed, and O(n) space complexity implementation is also available.
In this post, we’ll be implementing an algorithm that’d require no additional space as discussed in Set-1.

Below is the Algorithm:

• Create the copy of node 1 and insert it between node 1 & node 2 in the original Linked List, create a copy of 2 and insert it between 2 & 3. Continue in this fashion, add the copy of N after the Nth node
• Now copy the random link in this fashion
original->next->random= original->random->next;  /*TRAVERSE
TWO NODES*/
• This works because original->next is nothing but a copy of the original and Original->random->next is nothing but a copy of the random.

• 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;
• Ensure that original->next is NULL and return the cloned list

Below is the implementation.

## C++

 // C++ program to clone a linked list with next// and arbit pointers in O(n) time#include using namespace std; // Structure of linked list Nodestruct Node{    int data;    Node *next,*random;    Node(int x)    {        data = x;        next = random = NULL;    }}; // Utility function to print the list.void print(Node *start){    Node *ptr = start;    while (ptr)    {        cout << "Data = " << ptr->data << ", Random  = "             << ptr->random->data << endl;        ptr = ptr->next;    }} // This function clones a given linked list// in O(1) spaceNode* clone(Node *start){    Node* curr = start, *temp;     // insert additional node after    // every node of original list    while (curr)    {        temp = curr->next;         // Inserting node        curr->next = new Node(curr->data);        curr->next->next = temp;        curr = temp;    }     curr = start;     // adjust the random pointers of the    // newly added nodes    while (curr)    {        if(curr->next)            curr->next->random = curr->random ?                                 curr->random->next : curr->random;         // move to the next newly added node by        // skipping an original node        curr = curr->next?curr->next->next:curr->next;    }     Node* original = start, *copy = start->next;     // save the start of copied linked list    temp = copy;     // now separate the original list and copied list    while (original && copy)    {        original->next =         original->next? original->next->next : original->next;         copy->next = copy->next?copy->next->next:copy->next;        original = original->next;        copy = copy->next;    }     return temp;} // Driver codeint main(){    Node* start = new Node(1);    start->next = new Node(2);    start->next->next = new Node(3);    start->next->next->next = new Node(4);    start->next->next->next->next = new Node(5);     // 1's random points to 3    start->random = start->next->next;     // 2's random points to 1    start->next->random = start;     // 3's and 4's random points to 5    start->next->next->random =                    start->next->next->next->next;    start->next->next->next->random =                    start->next->next->next->next;     // 5's random points to 2    start->next->next->next->next->random =                                      start->next;     cout << "Original list : \n";    print(start);     cout << "\nCloned list : \n";    Node *cloned_list = clone(start);    print(cloned_list);     return 0;}

## Java

 // Java program to clone a linked list with next// and arbit pointers in O(n) timeimport java.util.*;import java.io.*; public class GfG {     // Structure of linked list Node    static class Node {        int data;        Node next, random;        Node(int x)        {            data = x;            next = random = null;        }    }     // Utility function to print the list.    static void print(Node start)    {        Node ptr = start;        while (ptr != null) {            System.out.println("Data = " + ptr.data                               + ", Random = "                               + ptr.random.data);            ptr = ptr.next;        }    }     // This function clones a given    // linked list in O(1) space    static Node clone(Node start)    {        Node curr = start, temp = null;         // insert additional node after        // every node of original list        while (curr != null) {            temp = curr.next;             // Inserting node            curr.next = new Node(curr.data);            curr.next.next = temp;            curr = temp;        }        curr = start;         // adjust the random pointers of the        // newly added nodes        while (curr != null) {            if (curr.next != null)                curr.next.random = (curr.random != null)                                       ? curr.random.next                                       : curr.random;             // move to the next newly added node by            // skipping an original node            curr = curr.next.next;                           }         Node original = start, copy = start.next;         // save the start of copied linked list        temp = copy;         // now separate the original list and copied list        while (original != null) {            original.next =original.next.next;           copy.next = (copy.next != null) ? copy.next.next                                            : copy.next;            original = original.next;            copy = copy.next;        }        return temp;    }     // Driver code    public static void main(String[] args)    {        Node start = new Node(1);        start.next = new Node(2);        start.next.next = new Node(3);        start.next.next.next = new Node(4);        start.next.next.next.next = new Node(5);         // 1's random points to 3        start.random = start.next.next;         // 2's random points to 1        start.next.random = start;         // 3's and 4's random points to 5        start.next.next.random = start.next.next.next.next;        start.next.next.next.random            = start.next.next.next.next;         // 5's random points to 2        start.next.next.next.next.random = start.next;         System.out.println("Original list : ");        print(start);         System.out.println("Cloned list : ");        Node cloned_list = clone(start);        print(cloned_list);    }} // This code is contributed by Prerna Saini.

## C#

 // C# program to clone a linked list with// next and arbit pointers in O(n) timeusing System; class GFG{ // Structure of linked list Nodeclass Node{    public int data;    public Node next, random;    public Node(int x)    {        data = x;        next = random = null;    }} // Utility function to print the list.static void print(Node start){    Node ptr = start;    while (ptr != null)    {        Console.WriteLine("Data = " + ptr.data +                          ", Random = " +                          ptr.random.data);        ptr = ptr.next;    }} // This function clones a given// linked list in O(1) spacestatic Node clone(Node start){    Node curr = start, temp = null;     // insert additional node after    // every node of original list    while (curr != null)    {        temp = curr.next;         // Inserting node        curr.next = new Node(curr.data);        curr.next.next = temp;        curr = temp;    }    curr = start;     // adjust the random pointers of    // the newly added nodes    while (curr != null)    {        if(curr.next != null)            curr.next.random = (curr.random != null)                    ? curr.random.next : curr.random;         // move to the next newly added node        // by skipping an original node        curr = (curr.next != null) ? curr.next.next                                        : curr.next;    }     Node original = start, copy = start.next;     // save the start of copied linked list    temp = copy;     // now separate the original list    // and copied list    while (original != null && copy != null)    {        original.next = (original.next != null)?                    original.next.next : original.next;         copy.next = (copy.next != null) ? copy.next.next                                             : copy.next;        original = original.next;        copy = copy.next;    }    return temp;} // Driver codepublic static void Main(String[] args){    Node start = new Node(1);    start.next = new Node(2);    start.next.next = new Node(3);    start.next.next.next = new Node(4);    start.next.next.next.next = new Node(5);     // 1's random points to 3    start.random = start.next.next;     // 2's random points to 1    start.next.random = start;     // 3's and 4's random points to 5    start.next.next.random = start.next.next.next.next;    start.next.next.next.random = start.next.next.next.next;     // 5's random points to 2    start.next.next.next.next.random = start.next;     Console.WriteLine("Original list : ");    print(start);     Console.WriteLine("Cloned list : ");    Node cloned_list = clone(start);    print(cloned_list);}} // This code has been contributed// by Rajput-Ji

## Javascript



Output

Original list :
Data = 1, Random  = 3
Data = 2, Random  = 1
Data = 3, Random  = 5
Data = 4, Random  = 5
Data = 5, Random  = 2

Cloned list :
Data = 1, Random  = 3
Data = 2, Random  = 1
Data = 3, Random  = 5
Data = 4, Random  = 5
Data = 5, Random  = 2

Time Complexity: O(n) As we are moving through the list thrice, i.e. 3n ,  but in asymptotic notations we drop the constant terms
Auxiliary Space: O(1) As no extra space is used. The n nodes which are inserted in between the nodes was already required to clone the list, so we can say that we did not use any extra space.

This article is contributed by Ashutosh Kumar 😀 If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.