/**
   * Unit tests the {@code DepthFirstOrder} data type.
   *
   * @param args the command-line arguments
   */
  public static void main(String[] args) {
    In in = new In(args[0]);
    Digraph G = new Digraph(in);

    DepthFirstOrder dfs = new DepthFirstOrder(G);
    StdOut.println("   v  pre post");
    StdOut.println("--------------");
    for (int v = 0; v < G.V(); v++) {
      StdOut.printf("%4d %4d %4d\n", v, dfs.pre(v), dfs.post(v));
    }

    StdOut.print("Preorder:  ");
    for (int v : dfs.pre()) {
      StdOut.print(v + " ");
    }
    StdOut.println();

    StdOut.print("Postorder: ");
    for (int v : dfs.post()) {
      StdOut.print(v + " ");
    }
    StdOut.println();

    StdOut.print("Reverse postorder: ");
    for (int v : dfs.reversePost()) {
      StdOut.print(v + " ");
    }
    StdOut.println();
  }