每日算法题: Reverse a Directed Graph

Hi, here's your problem today. This problem was recently asked by Facebook:

Given a directed graph, reverse the directed graph so all directed edges are reversed.

Example:
Input:
A -> B, B -> C, A ->C

Output:
B->A, C -> B, C -> A
Here's a starting point:

from collections import defaultdict



class Node:

  def __init__(self, value):

    self.adjacent = []

    self.value = value



def reverse_graph(graph):

  # Fill this in.



a = Node('a')

b = Node('b')

c = Node('c')



a.adjacent += [b, c]

b.adjacent += [c]



graph = {

    a.value: a,

    b.value: b,

    c.value: c,

}



for _, val in reverse_graph(graph).items():

  print(val.adjacent)

# []

# ['a', 'b']

# ['a']