Return dictionary of shortest path lengths between all nodes in G.
The dictionary only has keys for reachable node pairs. >>> G=nx.path_graph(5) >>> length=nx.all_pairs_shortest_path_length(G) >>> print length[1][4] 3 >>> length[1] {0: 1, 1: 0, 2: 1, 3: 2, 4: 3}
cutoff is optional integer depth to stop the search - only paths of length <= cutoff are returned.