public Vertex<T> dfs(Vertex<T> vertex, T targetData) {
        if (vertex.getData().equals(targetData)) {
            return vertex;
        }

        visited.add(vertex);
        for (Vertex<T> v: vertex.getVertexes()) {
            if (!visited.contains(v)) {
                dfs(v, targetData);
            }
        }
        return null;
    }