Returns the main chain node ID list.

def get_main_chain(self):
        """Returns the main chain node ID list."""
        pre_node = {}
        distance = {}
        for i in range(self.n_nodes):
            distance[i] = 0
            pre_node[i] = i
        for i in range(self.n_nodes - 1):
            for u in range(self.n_nodes):
                for v, _ in self.adj_list[u]:
                    if distance[u] + 1 > distance[v]:
                        distance[v] = distance[u] + 1
                        pre_node[v] = u
        temp_id = 0
        for i in range(self.n_nodes):
            if distance[i] > distance[temp_id]:
                temp_id = i
        ret = []
        for i in range(self.n_nodes + 5):
            ret.append(temp_id)
            if pre_node[temp_id] == temp_id:
                break
            temp_id = pre_node[temp_id]
        assert temp_id == pre_node[temp_id]
        ret.reverse()
        return ret