#!/usr/bin/python
# -*- coding=utf-8 -*-
# @Create Time:		2024-02-05 09:53:01
# @Last Modified time: 2024-02-21 13:09:15
class Digraph:
    def __init__(self, num):
        self.num_vertices = num
        self.num_edges = 0
        self.adj_list = [[] for _ in range(num)]

    def count_vertices(self):
        return self.num_vertices

    def count_edges(self):
        return self.num_edges

    def point_edge(self, x, y):
        self.adj_list[x].append(y)

    def point_to_vertices(self, x):
        return self.adj_list[x]

    def reverse_digraph(self):
        rvs_digraph = Digraph(self.num_vertices)
        for index, queue in enumerate(self.adj_list):
            for v in queue:
                rvs_digraph.point_edge(v, index)
        return rvs_digraph

if __name__ == '__main__':
    graph = Digraph(5)

    graph.point_edge(1, 2)
    graph.point_edge(2, 3)
    graph.point_edge(3, 4)
    graph.point_edge(2, 4)

    print(graph.point_to_vertices(2))
    print(graph.reverse_digraph().point_to_vertices(2))