Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

type vertexId int

type vertex struct {
	id vertexId
	firstVisitAt int
	finishVisitAt int
	adjs []vertexId
}

func createVertex(id int, adjsInt []int) vertex {
	adjs := make([]vertexId, len(adjsInt))
	for i := 0; i < len(adjs); i++ {
		adjs[i] = vertexId(adjsInt[i])
	}
	return vertex{
		id: vertexId(id),
		firstVisitAt: 0,
		finishVisitAt: 0,
		adjs: adjs,
	}
}

func (v *vertex) isVisited() bool {
	return v.firstVisitAt > 0
}

func dfs(currentId vertexId, timestamp int, vertices []vertex) int {
	currentVertex := &vertices[currentId-1]
	if currentVertex.isVisited() {
		return timestamp
	}
	timestamp = timestamp + 1
	currentVertex.firstVisitAt = timestamp
	for _, adjId := range currentVertex.adjs {
		timestamp = dfs(adjId, timestamp, vertices)
	}
	timestamp = timestamp + 1
	currentVertex.finishVisitAt = timestamp
	return timestamp
}

func solveDfs(vertices []vertex) {
	timestamp := 0
	for {
		vid := vertexId(-1)
		for i := 0; i < len(vertices); i++ {
			if !vertices[i].isVisited() {
				vid = vertexId(i+1)
				break
			}
		}
		if vid > 0 {
			timestamp = dfs(vid, timestamp, vertices)
		} else {
			break
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	vertices := make([]vertex, n)
	for i := 0; i < n; i++ {
		id, err := nextInt(sc)
		if err != nil {
			panic(err)
		}
		adjN, err := nextInt(sc)
		if err != nil {
			panic(err)
		}
		adjs := make([]int, adjN)
		for j := 0; j < adjN; j++ {
			adjId, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			adjs[j] = adjId
		}
		vertices[i] = createVertex(id, adjs)
	}

	solveDfs(vertices)

	for i := 0; i < n; i++ {
		fmt.Printf("%d %d %d\n", vertices[i].id, vertices[i].firstVisitAt, vertices[i].finishVisitAt)
	}
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

C++: #include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <climits>
#include <cstring>


using namespace std;

const int N_MAX = 1000000;
/*
bool update_num_to_visit(int st, int en, int* arr){
  if(st==-1) return false;
  arr[st]--;
  return arr[st]==0;
  }*/

int main(){
  int n;
  cin >> n;
  stack<pair<int, int> > edges;
  stack<pair<int, int> > paths;
  
  int** adjl = new int*[n];
  int* d = new int[n];
  int* f = new int[n];
  
  for(int i=0; i<n; i++){
    adjl[i] = new int[n];
    memset(adjl[i], -1, n * sizeof(adjl[i][0]));
  }
  
  memset(d, -1, n*sizeof(d[0]));
  memset(f, -1, n*sizeof(f[0]));

  for(int i=0; i<n; i++){
    int row_num, k;
    cin >> row_num >> k; row_num--;
    
    for(int j=0; j<k; j++){
      int node_num;
      cin >> node_num; node_num--;
      adjl[row_num][j] = node_num; // [[3, 5, -1 , ...], [1, 3, -1, ...], [1, 2], ...]
    }
  }

  for(int row_num=n-1; row_num>=0; row_num--){
      pair<int, int> p;
      p.first = -1; p.second = row_num; // visited from nowhere
      edges.push(p);
    }

  int time = 1;
  while(!edges.empty()){
    //    cout << "time: " << time << endl;
    
    pair<int, int> edge;
    edge = edges.top(); edges.pop();
    int st, en; st = edge.first; en = edge.second;
    //    cout << "visiting: " << en << " from: " << st << endl;
    
    pair<int, int> path; 
    // record path to go back
    if(st > -1){ // exclude (-1, node)
      path.first = en; path.second = st;
      // avoid inf loop: if the node is not finished, have to go back at some point
      if(f[path.second] == -1){
	paths.push(path);
	// cout << "<" << path.first << ", " << path.second << "> pushed as a path." << endl;
      }
    }    
    
    // if first time visit, mark as visited
    if(d[en] == -1) d[en] = time;
    
    // if not first time, check if it was finished.
    // if it was already finished, continue
    if(f[en] != -1){
      continue;
    }
    
    // counter for opened nodes
    int unvisited_node_num = 0;

    // open node (reverse order)
    for(int i=n-1; i>=0; i--){
      int next_node = adjl[en][i];
      // cout << "next_node: " << next_node << endl;
      // undefined dest or visited, continue
      if(next_node == -1) continue;
      if(d[next_node] != -1){
	// if num_to_visit[en] > 0;
	continue;
      }
      // if unvisited, push into stack
      unvisited_node_num++;
      pair<int, int> next_edge; next_edge.first = en; next_edge.second = next_node;
      edges.push(next_edge);
      // cout << "<" << next_edge.first << ", " << next_edge.second << "> pushed." << endl;
    }

    // if there are no unvisited linked nodes anymore, mark the node finished
    if(unvisited_node_num == 0){
      // cout << "going back..." << endl;
      f[en] = time + 1;
      // cout << "f[" << en << "]: " << f[en] << endl;
      
      // way to go back
      if(paths.empty()) break;
      path = paths.top(); paths.pop();
      edges.push(path);
      // cout << "path pushed." << endl;
    }
    time++;
  }

  // print 'i+1, d[i], f[i]'
  
  for(int i=0; i<n; i++){
    cout << i+1 << " " << d[i] << " " << f[i] << endl;
  }
  
  for(int i=0; i<n; i++){
    delete[] adjl[i];
  }
  delete[] adjl;
  delete[] d;
  delete[] f;
  
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <set>
#include <unordered_map>
//#include "../cxx-prettyprint/prettyprint.hpp"

int timer = 0;
std::unordered_map<int, std::vector<int>> Adj;
std::set<int> nodes_unvisited;
std::unordered_map<int, int> discovered_time;
std::unordered_map<int, int> finished_time;

int dfs(int u) {
    nodes_unvisited.erase(u);
    discovered_time[u] = ++timer;
    for (int v : Adj[u]) {
        if (nodes_unvisited.find(v) != nodes_unvisited.end()) {
            dfs(v);
        }
    }
    finished_time[u] = ++timer;
}

int main() {
    int n;
    std::cin >> n;

    for (int i = 0; i < n; i ++) {
        int u, k;
        std::cin >> u >> k;
        std::vector<int> V(k);
        for (auto& v : V) {
            std::cin >> v;
        }
        Adj[u] = V;
    }

    for (int i = 1; i <= n; i ++) {
        nodes_unvisited.insert(i);
    }

    while (!nodes_unvisited.empty()) {
        int u = *nodes_unvisited.begin();
        dfs(u);
    }

    for (int i = 1; i <= n; i ++) {
        std::cout << i << " " << discovered_time[i]
            << " " << finished_time[i] << std::endl;
    }
}