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:

Input : Head of the below linked list


Output :
A new linked listidentical 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 original Linked List, create the copy of 2 and insert it between 2 & 3.. Continue in this fashion, add the copy of N afte 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 copy of original and Original->random->next is nothing but copy of 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++

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// 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;
}

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Java

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// 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 != 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; 
  
    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.

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C#

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// 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

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Python

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'''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'''

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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

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