Clone a graph

"""
# 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 collections import deque
class Solution:

    def cloneGraph(self, node: 'Node') -> 'Node':
        if node==None:
            return None
        elif len(node.neighbors)==0:
            return Node(node.val)
        q=deque()
        q.append(node)
        d={}
        d[node.val]=Node(node.val)
        while q:
            top=q.popleft()
            for nei in top.neighbors:
                if nei.val not in d:
                    d[nei.val]=Node(nei.val)
                    d[top.val].neighbors.append(d[nei.val])
                    q.append(nei)
                else:
                    d[top.val].neighbors.append(d[nei.val])
        return d[node.val]