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

  • Difficulty Level : Hard
  • Last Updated : 14 Jun, 2021

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: 
 

Input : Head of the below-linked list

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 <bits/stdc++.h>
using namespace std;
 
// Structure of linked list Node
struct 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) space
Node* 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 code
int 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) time
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) time
using System;
 
class GFG
{
 
// Structure of linked list Node
class 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) 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 != 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 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;
 
    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

Python




'''Python program to clone a linked list with next and arbitrary pointers'''
'''Done in O(n) time with O(1) extra space'''
 
class Node:
    '''Structure of linked list node'''
 
    def __init__(self, data):
        self.data = data
        self.next = None
        self.random = None
 
def clone(original_root):
    '''Clone a doubly linked list with random pointer'''
    '''with O(1) extra space'''
 
    '''Insert additional node after every node of original list'''
    curr = original_root
    while curr != None:
        new = Node(curr.data)
        new.next = curr.next
        curr.next = new
        curr = curr.next.next
 
    '''Adjust the random pointers of the newly added nodes'''
    curr = original_root
    while curr != None:
        curr.next.random = curr.random.next
        curr = curr.next.next
 
    '''Detach original and duplicate list from each other'''
    curr = original_root
    dup_root = original_root.next
    while curr.next != None:
        tmp = curr.next
        curr.next = curr.next.next
        curr = tmp
 
    return dup_root
 
def print_dlist(root):
    '''Function to print the doubly linked list'''
 
    curr = root
    while curr != None:
        print('Data =', curr.data, ', Random =', curr.random.data)
        curr = curr.next
 
####### Driver code #######
'''Create a doubly linked list'''
original_list = Node(1)
original_list.next = Node(2)
original_list.next.next = Node(3)
original_list.next.next.next = Node(4)
original_list.next.next.next.next = Node(5)
 
'''Set the random pointers'''
 
# 1's random points to 3
original_list.random = original_list.next.next
 
# 2's random points to 1
original_list.next.random = original_list
 
# 3's random points to 5
original_list.next.next.random = original_list.next.next.next.next
 
# 4's random points to 5
original_list.next.next.next.random = original_list.next.next.next.next
 
# 5's random points to 2
original_list.next.next.next.next.random = original_list.next
 
'''Print the original linked list'''
print('Original list:')
print_dlist(original_list)
 
'''Create a duplicate linked list'''
cloned_list = clone(original_list)
 
'''Print the duplicate linked list'''
print('\nCloned list:')
print_dlist(cloned_list)
 
'''This code is contributed by Shashank Singh'''

Javascript




<script>
 
// Javascript program to clone a linked list with next
// and arbit pointers in O(n) time
 
 
    // Structure of linked list Node
     class Node {
 
constructor(x) {
            this.data = x;
            this.next = this.random = null;
        }
    }
 
    // Utility function to print the list.
    function print(start) {
var ptr = start;
        while (ptr != null) {
            document.write(
            "Data = " +
            ptr.data + ", Random = "
            + ptr.random.data+"<br/>"
            );
            ptr = ptr.next;
        }
    }
 
    // This function clones a given
    // linked list in O(1) space
    function clone(start) {
var 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;
        }
 
var 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 code
     
var 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;
 
        document.write("Original list : <br/>");
        print(start);
        document.write("<br>");
        document.write("Cloned list : <br/>");
        var cloned_list = clone(start);
        print(cloned_list);
 
 
// This code contributed by aashish1995
 
</script>
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

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.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 

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