In this post, we are going to solve the 138. Copy List with Random Pointer problem of Leetcode. This problem 138. Copy List with Random Pointer is a Leetcode medium level problem. Let’s see code, 138. Copy List with Random Pointer – Leetcode Solution.

Problem

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null.

Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes, where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list.

For example, if there are two nodes X and Y in the original list, where X.random --> Y, then for the corresponding two nodes x and y in the copied list, x.random --> y.

Return the head of the copied linked list.

The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

• val: an integer representing Node.val
• random_index: the index of the node (range from 0 to n-1) that the random pointer points to, or null if it does not point to any node.

Your code will only be given the head of the original linked list.

Example 1 :

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

Example 2 :

Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]

Example 3 :

Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]

Constraints

• 0 <= n <= 1000
• -104 <= Node.val <= 104
• Node.random is null or is pointing to some node in the linked list.

Now, let’s see the code of 138. Copy List with Random Pointer – Leetcode Solution.

Copy List with Random Pointer – Leetcode Solution

138. Copy List with Random Pointer – Solution in Java

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/

class Solution {
    
    public void copyList(Node head){

        Node curr = head;
        while(curr != null){
            Node forw = curr.next;
            
            Node node = new Node(curr.val);
            curr.next = node;
            node.next = forw;
            
            curr = forw;
        }

    }
    
    public void setRandomPointer(Node head){
        
        Node curr = head;
        while(curr != null){
            Node rnd = curr.random;
            if(rnd != null){
                curr.next.random = rnd.next;
            }
              curr = curr.next.next;
            
        }
        
    }
    
    public Node deepCopyList(Node head){
        
        Node dummy = new Node(-1);
        Node prev = dummy;
        Node curr = head;
        
        while(curr != null){
            prev.next = curr.next;
            curr.next = curr.next.next;
            
            prev = prev.next;
            curr = curr.next;
        }
        
        return dummy.next;
    }
    
    public Node copyRandomList(Node head) {
        copyList(head);
        setRandomPointer(head);
        Node ans = deepCopyList(head);
        return ans;
    }
}

138. Copy List with Random Pointer – Solution in C++

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* next;
    Node* random;
    
    Node(int _val) {
        val = _val;
        next = NULL;
        random = NULL;
    }
};
*/

class Solution {
public:
    Node* copyRandomList(Node* head) {
        if(head==NULL)
        {
            return head;
        }
        Node* temp=head;
        Node* deep;
        Node* step;
        while(temp!=NULL)
        {
            deep=new Node(temp->val);
            step=temp->next;
            temp->next=deep;
            deep->next=step;
            temp=temp->next->next;
        }
        temp=head;
        Node* ans=head->next;
        step=ans;
        while(temp!=NULL)
        {
            if(temp->random==NULL)
            {
                temp->next->random=temp->random;
            }
            else
            {
                temp->next->random=temp->random->next;
            }
            temp=temp->next->next;
        }
        temp=head;
        while(temp!=NULL)
        {
            temp->next=temp->next->next;
            temp=temp->next;
            if(temp!=NULL)
            {
                ans->next=temp->next;
            }
            ans=ans->next;
        }
        return step;
    }
};

138. Copy List with Random Pointer – Solution in Python

"""
# Definition for a Node.
class Node:
    def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):
        self.val = int(x)
        self.next = next
        self.random = random
"""

class Solution:
    def copyRandomList(self, head: 'Optional[Node]') -> 'Optional[Node]':
        iter=head
        front=head
        while iter != None:
            front= iter.next
            copy=Node(iter.val)
            iter.next=copy
            copy.next=front
            iter=front
        iter=head
        while iter != None:
            if iter.random != None:
                iter.next.random=iter.random.next
            iter=iter.next.next
        iter=head
        phead=Node(0)
        copy=phead
        while iter != None:
            front=iter.next.next
            copy.next=iter.next
            copy=copy.next
            iter.next=front
            iter=front
        return phead.next  
        

Note: This problem 138. Copy List with Random Pointer is generated by Leetcode but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.