LeetCode - Copy List with Random Pointer

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.

 

My Solution:

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

class Solution(object):
    def copyRandomList(self, head):
        """
        :type head: Node
        :rtype: Node
        """

        if not head:
            return None
        
        next_list = [head]
        node = head
        while node.next:
            if node.next in next_list:
                break
            next_list.append(node.next)
            node = node.next
        
        random_indexes = []
        for node in next_list:
            random_indexes.append(None if node.random is None else next_list.index(node.random))

        copy_head = Node(head.val)
if len(next_list) == 1:
            copy_head.next = None if head.next is None else copy_head
            copy_head.random = None if head.random is None else copy_head
            return copy_head

        copy_list = []
        node = copy_head
        for i in range(len(next_list)):
            node.next = None if i == len(next_list) - 1 else Node(next_list[i + 1].val)
            copy_list.append(node)
            node = node.next
        
        for i in range(len(copy_list)):
            copy_list[i].random = None if random_indexes[i] is None else copy_list[random_indexes[i]]

        return copy_head

 

 

ChatGPT's Solution:

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

class Solution(object):
    def copyRandomList(self, head):
        """
        :type head: Node
        :rtype: Node
        """

        if not head:
            return None
        
        # Step 1: Create new nodes and interweave them with original nodes
        curr = head
        while curr:
            new_node = Node(curr.val, curr.next)
            curr.next = new_node
            curr = new_node.next
        
        # Step 2: Assign random pointers for the new nodes
        curr = head
        while curr:
            if curr.random:
                curr.next.random = curr.random.next
            curr = curr.next.next
        
        # Step 3: Separate the original and copied list
        curr = head
        new_head = head.next
        copy_curr = new_head
        while curr:
            curr.next = curr.next.next
            copy_curr.next = copy_curr.next.next if copy_curr.next else None
            curr = curr.next
            copy_curr = copy_curr.next
        
        return new_head