在Python中表示此图

class Graph:
    def __init__(self, num_nodes):
        self.num_nodes = num_nodes
        self.matrix = [[0] * num_nodes for _ in range(num_nodes)]
    
    def add_edge(self, i, j):
        self.matrix[i][j] = 1
        self.matrix[j][i] = 1

class Node:
    def __init__(self, value):
        self.value = value
        self.neighbors = []

class Graph:
    def __init__(self):
        self.nodes = []
    
    def add_edge(self, i, j):
        node_i = self.get_node(i)
        node_j = self.get_node(j)
        node_i.neighbors.append(node_j)
        node_j.neighbors.append(node_i)
    
    def get_node(self, value):
        for node in self.nodes:
            if node.value == value:
                return node
        new_node = Node(value)
        self.nodes.append(new_node)
        return new_node