public void printGraph() {
        for (int i = 0; i < this.vertices.size(); i++) {
            DirectedNode vertex = this.vertices.get(i);
            String edges = "";
            for (int j = 0; j < vertex.edgeNodes.size(); j++) {
                edges += vertex.edgeNodes.get(j).data + ", ";
            }
            System.out.println("Vertex " + vertex.data + " connects with: " + edges);
        }
    }