广度优先遍历-python

主体代码模板：

from collections import deque # 使用双端队列deque，Queue更为复杂不可用

def bfs():
    queue = deque([root])   # 队列数据结构实现
    visited = set(root)     # 标记访问节点
    while queue:
        cur_node = queue.popleft()
        for neighbor in cur_node.neighbors:
            if neighbor in visited:
                continue
            queue.append(neighbor)
            visited.add(neighbor)
    return list(visited)