unreasonably effective

"""
# Definition for a Node.
class Node:
    def __init__(self, val = 0, neighbors = None):
        self.val = val
        self.neighbors = neighbors if neighbors is not None else []
"""

from typing import Optional
class Solution:
    def copy_node(self, u, map):
        map[u] = map.get(u, Node(u.val))
        for v in u.neighbors:
            map[v] = map.get(v, Node(v.val))
            map[u].neighbors.append(map[v])

    def explore(self, u, map, visited):
        self.copy_node(u, map)
        visited.add(u)
        for v in u.neighbors:
            if v in visited:
                continue
            self.explore(v, map, visited)

    def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
        if not node:
            return None
        map = {}
        self.explore(node, map, set())
        return map[node]