def find_one_path(graph, start, end, path=[]):
    """
    寻找graph中由start到end顶点的其中一条路径
    graph: dict
    start: str
    end: str
    return: list
    """
    path = path + [start]
    if start == end:
        return path
    if start not in graph.keys():
        return None
    for node in graph[start]:
        if node not in path:  # 保证路径的顶点不重复
            new_path = find_one_path(graph, node, end, path)
            if new_path:
                return new_path
    return path