Language: C++

#include<iostream>
#include<stack>

using namespace std;

int  n, M[100][100], d[100], f[100], color[100], time, nt[100], W = 0, G = 1, B = 2;

int next (int u) {

    int v;
    for (v = nt[u]; v < n; v++) {
        nt[u] = v + 1;
        if (M[u][v] != 0) {
            return v;
        }
    }
    return -1;

}

void dfs_visit (int r) {

    int i, u, v;

    for (i = 0; i < n; i++) {
        nt[i] = 0;
    }

    stack<int> S;
    S.push(r);
    color[r] = G;
    d[r] = ++time;

    while (!S.empty()) {
        u = S.top();
        v = next (u);
        if (v != -1) {
            if (color[v] == W) {
                color[v] = G;
                d[v] = ++time;
                S.push(v);
            }
        } else {
            S.pop();
            color[u] = B;
            f[u] = ++time;
        }
    }

}

void dfs () {

    int i, u;

    for (i = 0; i < n; i++) {
        color[i] = W;
        nt[i] = 0;
    }
    time = 0;

    for (u = 0; u < n; u++) {
        if (color[u] == W) {
            dfs_visit(u);
        }
    }

    for (i = 0; i < n; i++) {
        cout << i + 1 << " " << d[i] << " " << f[i] << endl;
    }

}

int main () {

    int u, k, v, i, j;

    cin >> n;
    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++) {
            M[i][j] = 0;
        }
    }

    for (i = 0; i < n; i++) {
        cin >> u >> k;
        u--;
        for (j = 0; j < k; j++) {
            cin >> v;
            v--;
            M[u][v] = 1;
        }
    }

    dfs ();

    return 0;

}

Compiler output:
a.cc:6:50: error: 'int time' redeclared as different kind of entity
    6 | int  n, M[100][100], d[100], f[100], color[100], time, nt[100], W = 0, G = 1, B = 2;
      |                                                  ^~~~
In file included from /usr/include/pthread.h:23,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/gthr-default.h:35,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/gthr.h:157,
                 from /usr/include/c++/14/ext/atomicity.h:35,
                 from /usr/include/c++/14/bits/ios_base.h:39,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/time.h:76:15: note: previous declaration 'time_t time(time_t*)'
   76 | extern time_t time (time_t *__timer) __THROW;
      |               ^~~~
a.cc: In function 'void dfs_visit(int)':
a.cc:32:14: warning: ISO C++ forbids incrementing a pointer of type 'time_t (*)(time_t*) noexcept' {aka 'long int (*)(long int*) noexcept'} [-Wpointer-arith]
   32 |     d[r] = ++time;
      |              ^~~~
a.cc:32:14: error: lvalue required as increment operand
a.cc:40:26: warning: ISO C++ forbids incrementing a pointer of type 'time_t (*)(time_t*) noexcept' {aka 'long int (*)(long int*) noexcept'} [-Wpointer-arith]
   40 |                 d[v] = ++time;
      |                          ^~~~
a.cc:40:26: error: lvalue required as increment operand
a.cc:46:22: warning: ISO C++ forbids incrementing a pointer of type 'time_t (*)(time_t*) noexcept' {aka 'long int (*)(long int*) noexcept'} [-Wpointer-arith]
   46 |             f[u] = ++time;
      |                      ^~~~
a.cc:46:22: error: lvalue required as increment operand
a.cc: In function 'void dfs()':
a.cc:60:10: error: assignment of function 'time_t time(time_t*)'
   60 |     time = 0;
      |     ~~~~~^~~