138. Copy-List-with-Random-Pointer

"""
# 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]':
        
        hash_map = {}
        def helper(head):
            if not head:
                return None
            if head in hash_map:
                return hash_map[head]
            hash_map[head] = Node(head.val)
            hash_map[head].next = helper(head.next)
            hash_map[head].random = helper(head.random)
            return hash_map[head]

        
        return helper(head)