Search for all the layers and nodes down the path.
        A recursive function to search all the layers and nodes between the node in the node_list
            and the node with target_id.

def _depth_first_search(self, target_id, layer_id_list, node_list):
        """Search for all the layers and nodes down the path.
        A recursive function to search all the layers and nodes between the node in the node_list
            and the node with target_id."""
        assert len(node_list) <= self.n_nodes
        u = node_list[-1]
        if u == target_id:
            return True

        for v, layer_id in self.adj_list[u]:
            layer_id_list.append(layer_id)
            node_list.append(v)
            if self._depth_first_search(target_id, layer_id_list, node_list):
                return True
            layer_id_list.pop()
            node_list.pop()

        return False