问求节点的n次邻域

EN

import networkx as nx
G = nx.Graph()
G.add_edges_from([('v1','v2'),('v2','v4'),('v1','v3')])

def neighborhood(G, node, n):
    path_lengths = nx.single_source_dijkstra_path_length(G, node)
    return [node for node, length in path_lengths.iteritems()
                    if length == n]

print(neighborhood(G, 'v1', 1))
# ['v2', 'v3']
print(neighborhood(G, 'v1', 2))
# ['v4']

import networkx as nx

def n_neighbor(G, start):

    #  {distance : [list of nodes at that distance]}
    distance_nodes = {}

    # nodes at distance 1 from the currently visited ones
    next_shell = G.neighbors(start)

    # set of all visited nodes
    visited=set()
    visited.add(start)

    # how fare we are from start
    distance = 0

    # until we run out of nodes
    while len(next_shell) > 0:

        # this will be the next shell
        shell_after_this = []

        # update distance
        distance += 1
        distance_nodes[distance] = []

        # update visited and distance_nodes
        for node in next_shell:
            visited.add(node)
            distance_nodes[distance].append(node)


        # compute shell_after_this
        for node in next_shell:
            # add neighbors to shell_after_this
            # if they have not been visited already
            for neighbor in G.neighbors(node):
                if neighbor not in visited:
                    shell_after_this.append(neighbor)

        # we repeat with the new_shell
        next_shell = set(shell_after_this)

    return distance_nodes


# example 
G=nx.Graph()

G.add_edge(1,2)
G.add_edge(1,3)
G.add_edge(2,3)
G.add_edge(2,4)
G.add_edge(3,5)
G.add_edge(5,17)
G.add_edge(2,6)

print n_neighbor(G, 1)