Problem p03921 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <array>
#include <bitset>
#include <chrono>
#include <cmath>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
typedef unsigned long long int ulint;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
#define RE return 0
// ios::sync_with_stdio(false);
// std::cin.tie(0);
//<< setprecision(20)
const int mod = 1e9 + 7;
const llint big = 1e15 + 100;
const long double pai = 3.141592653589793238462643383279502884197;
const long double ena = 2.71828182845904523536;
const long double eps = 1e-7;
template <class T, class U> void mineq(T &a, U b) {
  if (a > b) {
    a = b;
  }
}
template <class T, class U> void maxeq(T &a, U b) {
  if (a < b) {
    a = b;
  }
}
template <class T> void soun(T &ar) {
  sort(ar.begin(), ar.end());
  ar.erase(unique(ar.begin(), ar.end()), ar.end());
}
llint gcd(llint a, llint b) {
  if (a % b == 0) {
    return b;
  } else {
    return gcd(b, a % b);
  }
}
llint lcm(llint a, llint b) { return a / gcd(a, b) * b; }
template <class T, class U> auto LB(T &ve, U in) {
  return lower_bound(ve.begin(), ve.end(), in);
}
template <class T, class U> auto UB(T &ve, U in) {
  return upper_bound(ve.begin(), ve.end(), in);
}
template <class T, class U> auto LBI(T &ve, U in) {
  return LB(ve, in) - ve.begin();
}
template <class T, class U> auto UBI(T &ve, U in) {
  return UB(ve, in) - ve.begin();
}
template <class T> void SO(T &ve) { sort(ve.begin(), ve.end()); }
int main(void) {
  int n, m, i, j, ans = 0;
  cin >> n >> m;
  vector<vector<int>> hana(m);
  vector<vector<int>> spe(n);
  vector<bool> koto(m);
  vector<bool> hito(n);
  for (i = 0; i < n; i++) {
    int k;
    cin >> k;
    while (k--) {
      int L;
      cin >> L;
      L--;
      hana[L].pub(i);
      spe[i].pub(L);
    }
  }
  queue<int> que;
  que.push(hana[0][0]);
  while (que.size() > 0) {
    int gen = que.front();
    que.pop();
    if (koto[gen]) {
      continue;
    }
    koto[gen] = true;
    for (auto it : hana[gen]) {
      if (hito[it]) {
        continue;
      }
      hito[it] = true;
      ans++;
      for (auto itr : spe[it]) {
        que.push(itr);
      }
    }
  }
  cout << (ans == n ? "YES" : "NO") << endl;
  RE;
}


Fixed submission:
#include <algorithm>
#include <array>
#include <bitset>
#include <chrono>
#include <cmath>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
typedef unsigned long long int ulint;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
#define RE return 0
// ios::sync_with_stdio(false);
// std::cin.tie(0);
//<< setprecision(20)
const int mod = 1e9 + 7;
const llint big = 1e15 + 100;
const long double pai = 3.141592653589793238462643383279502884197;
const long double ena = 2.71828182845904523536;
const long double eps = 1e-7;
template <class T, class U> void mineq(T &a, U b) {
  if (a > b) {
    a = b;
  }
}
template <class T, class U> void maxeq(T &a, U b) {
  if (a < b) {
    a = b;
  }
}
template <class T> void soun(T &ar) {
  sort(ar.begin(), ar.end());
  ar.erase(unique(ar.begin(), ar.end()), ar.end());
}
llint gcd(llint a, llint b) {
  if (a % b == 0) {
    return b;
  } else {
    return gcd(b, a % b);
  }
}
llint lcm(llint a, llint b) { return a / gcd(a, b) * b; }
template <class T, class U> auto LB(T &ve, U in) {
  return lower_bound(ve.begin(), ve.end(), in);
}
template <class T, class U> auto UB(T &ve, U in) {
  return upper_bound(ve.begin(), ve.end(), in);
}
template <class T, class U> auto LBI(T &ve, U in) {
  return LB(ve, in) - ve.begin();
}
template <class T, class U> auto UBI(T &ve, U in) {
  return UB(ve, in) - ve.begin();
}
template <class T> void SO(T &ve) { sort(ve.begin(), ve.end()); }
int main(void) {
  int n, m, i, j, ans = 0;
  cin >> n >> m;
  vector<vector<int>> hana(m);
  vector<vector<int>> spe(n);
  vector<bool> koto(m);
  vector<bool> hito(n);
  for (i = 0; i < n; i++) {
    int k;
    cin >> k;
    while (k--) {
      int L;
      cin >> L;
      L--;
      hana[L].pub(i);
      spe[i].pub(L);
    }
  }
  queue<int> que;
  que.push(spe[0][0]);
  while (que.size() > 0) {
    int gen = que.front();
    que.pop();
    if (koto[gen]) {
      continue;
    }
    koto[gen] = true;
    for (auto it : hana[gen]) {
      if (hito[it]) {
        continue;
      }
      hito[it] = true;
      ans++;
      for (auto itr : spe[it]) {
        que.push(itr);
      }
    }
  }
  cout << (ans == n ? "YES" : "NO") << endl;
  RE;
}