#!/usr/bin/env python
#-*- coding:utf-8 -*-
'''
ADT Graph:
    Graph(self)
    is_empty(self)
    vertex_num(self)    #Get the number of vertices
    edge_num(self)
    vertices(self)      #Get the set of all vertivces
    edges(self)         #Get the set of all edges
    add_vertex(self, vertex)    #Insert a new vertex
    add_edge(self, v1, v2)      #Add an edge between v1 and v2
    get_edge(self, v1, v2)      #Get weight of specific edge
    out_edges(self, v)          #Get all edges from v
    degree(self, v)             
'''