# 15.Copy List with Random Pointer

Return a **deep copy** of the list.

![Example ](/files/-MHqDAUkX3t6mFWxkdtk)

```
Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]
```

## Solution I :(Using Extra Space)

**Algorithm:**\
1\. Create all nodes in **copy linked list** using next pointers.\
2\. **Store** the **next pointer mappings of original linked list**.\
4\. Make the **random pointer of copy linked list point to original Linked List.**\
5\. Make the **Next pointer of the original Linked List point to copy linked list.**\
6\. **Set the random pointer of copy linked list to original values using** \
                 **node->random = node->random->random->next**\
7.Change **next pointer of all nodes in original linked list** to point to the corresponding node in linked list.

![](/files/-MHqGrDJStfmBFODEQRw)

```cpp
class Solution
{
public:
    Node *copyRandomList(Node *head)
    {
        
        if(head == NULL){return NULL;}

        vector<Node *> v;

        Node *head1 = NULL;
        Node *p = head;
        Node *q = NULL;
        Node *t = NULL;

        // Creating a copy of original ll
        while (p != NULL)
        {
            Node *temp = new Node(p->val);
            if (head1 == NULL)
            {
                head1 = temp;
                t = head1;
            }
            else
            {
                t->next = temp;
                t = t->next;
            }
            p = p->next;
            // Store the original address
            v.push_back(p);
        }

        //changing random pointer
        p = head;
        t = head1;
        while (p != NULL)
        {
            t->random = p;
            p = p->next;
            t = t->next;
        }

        //changing next pointer
        p = head;
        q = head;
        t = head1;
        while (p != NULL)
        {
            p = p->next;
            q->next = t;
            q = p;
            t = t->next;
        }

        //assigning random pointer its correct value
        t = head1;
        while (t != NULL)
        {
            if (t->random->random != NULL)
            {
                t->random = t->random->random->next;
            }
            else
            {
                t->random = NULL;
            }

            t = t->next;
        }

         // Restore the original next pointer
        p = head;
        for (int i = 0; i < v.size(); i++)
        {
            p->next = v[i];
            p = p->next;
        }

        return head1;
    }
};
```

**Time Complexity: O(n) , Space Complexity: O(n)**

## Solution II: (Using Constant Space)

**Algorithm :**

* Create the copy of node 1 and insert it between node 1 & node 2 in 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 nod&#x65;**.**

![](/files/-MHyNUZGu9-nT8j5-bLz)

* Now copy the random link:

```
 original->next->random= original->random->next
```

![](/files/-MHyNosVXBJlunUfYsjH)

* 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;
```

![](/files/-MHyOIcXlBbSmhnKnAnk)

```cpp
class Solution
{
public:
    Node *copyRandomList(Node *head)
    {

        if (head == NULL)
        {
            return head;
        }

        Node *p = head;
        Node *q = head;

        //Inserting a copy in between original values
        while (p != NULL)
        {
            q = p->next;
            Node *temp = new Node(p->val);
            p->next = temp;
            temp->next = q;
            p = q;
        }

        //Copying the random pointers
        p = head;
        while (p)
        {
            if (p->random)
            {
                p->next->random = p->random->next;
            }
            else
            {
                p->next->random = NULL;
            }

            if (p->next)
            {
                p = p->next->next;
            }
            else
            {
                p = p->next;
            }
        }

        //Separting original and random pointers
        Node *orgi = head;
        Node *copy = head->next;
        Node *temp = copy;

        while (orgi && copy)
        {
            if (orgi->next)
            {
                orgi->next = orgi->next->next;
            }
            else
            {
                orgi->next = NULL;
            }

            if (copy->next)
            {
                copy->next = copy->next->next;
            }
            else
            {
                copy->next = NULL;
            }

            orgi = orgi->next;
            copy = copy->next;
        }

        return temp;
    }
};
```

**Time Complexity: O(n)**


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://soumyajit4419.gitbook.io/ds-algo/linked-list/12.copy-list-with-random-pointer.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.