https://leetcode.com/problems/copy-list-with-random-pointer/

copy_list_with_random.py

class Solution:
    def copyRandomList(self, head: 'Optional[Node]') -> 'Optional[Node]':
        old_to_new = {}
        
        def clone_node(node):
            if not node:
                return None
            if node in old_to_new:
                return old_to_new[node]
            new_node = Node(node.val)
            old_to_new[node] = new_node
            new_node.random = clone_node(node.random)
            new_node.next = clone_node(node.next)
            return new_node

        return clone_node(head)