Leetcode 133.了解dfs的克隆图

# 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 []

class Solution:
    def cloneGraph(self, node: 'Node') -> 'Node':
        if not node:
            return None
        
        visited = {}
        return self.dfs(node, visited)
    
    def dfs(self, node, visited):
        if node in visited:
            return visited[node]
        
        clone = Node(node.val)
        visited[node] = clone
        
        for neighbor in node.neighbors:
            clone.neighbors.append(self.dfs(neighbor, visited))
        
        return clone