Problem p02991 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cmath>
#include <iostream>
#include <numeric>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std;
using ll = long long;

void _cin() {}
template <class Head, class... Tail> void _cin(Head &&head, Tail &&...tail) {
  cin >> head;
  _cin(forward<Tail>(tail)...);
}
void _cout() { cout << "\n"; }
template <class Head, class... Tail> void _cout(Head &&head, Tail &&...tail) {
  cout << head;
  _cout(forward<Tail>(tail)...);
}
int gcd(int a, int b) { return (b == 0) ? a : gcd(b, a % b); }

#define Sq(x) (x) * (x)
#define For(i, n) for (int i = 0; i < (n); i++)
#define Rep(n) For(_, n)
#define Range(c) c.begin(), c.end()
#define RevRange(c) c.rbegin(), c.rend()
#define Contains(c, x) (find(Range(c), x) != c.end())
#define Search(rb, re, x) distance(rb, find(rb, re, x))
#define Sort(a) sort(Range(a))
#define DeSort(a) sort(RevRange(a))
#define Reverse(c) reverse(Range(c))
#define Unique(a) a.erase(unique(Range(a)), a.end())
#define Cusum(T, xs, sxs)                                                      \
  vector<T> sxs(xs.size() + 1);                                                \
  For(i, (int)xs.size()) sxs[i + 1] = sxs[i] + xs[i]
#define Cin(T, ...)                                                            \
  T __VA_ARGS__;                                                               \
  _cin(__VA_ARGS__)
#define Cins(T, n, xs)                                                         \
  vector<T> xs(n);                                                             \
  For(i, n) cin >> xs[i]
#define Cins2(T, n, xs, ys)                                                    \
  vector<T> xs(n), ys(n);                                                      \
  For(i, n) cin >> xs[i] >> ys[i]
#define Cins3(T, n, xs, ys, zs)                                                \
  vector<T> xs(n), ys(n), zs(n);                                               \
  For(i, n) cin >> xs[i] >> ys[i] >> zs[i]
#define Cinss(T, n, m, xs)                                                     \
  Vec2(T, n, m, xs);                                                           \
  For(i, n) For(j, m) cin >> xs[i][j]
#define Cinm(T, n, map)                                                        \
  unordered_map<T, int> map;                                                   \
  Rep(n) {                                                                     \
    Cin(T, x);                                                                 \
    map[x]++;                                                                  \
  }
#define Cout(...) _cout(__VA_ARGS__)
#define Couts(xs)                                                              \
  {                                                                            \
    for (const auto &e : xs)                                                   \
      cout << e << " ";                                                        \
    cout << "\n";                                                              \
  }
#define Coutyn(cond) Cout((cond) ? "yes" : "no")
#define CoutYn(cond) Cout((cond) ? "Yes" : "No")
#define CoutYN(cond) Cout((cond) ? "YES" : "NO")
#define vc vector
#define Mini(a, x) a = min(a, x)
#define Maxi(a, x) a = max(a, x)

// constexpr int MOD = 1e9+7;
#include <queue>

int main(void) {
  Cin(int, n, m);
  vc<vc<int>> a(n, vc<int>()), b(n, vc<int>());
  Rep(m) {
    Cin(int, u, v);
    u--, v--;
    a[u].push_back(v);
  }
  Cin(int, s, t);
  s--, t--;

  auto f = [&](vc<int> v) {
    vc<int> r;
    vc<bool> e(n);
    for (int i : v)
      for (int j : a[i]) {
        if (!e[j])
          e[j] = true, r.push_back(j);
      }
    return r;
  };
  For(i, n) b[i] = f(f(f({i})));

  constexpr int Inf = 2e9;
  vc<int> d(n, Inf);
  d[s] = 0;

  using P = pair<int, int>;
  priority_queue<P, vector<P>, greater<P>> q;
  q.emplace(0, s);
  while (!q.empty()) {
    auto e = q.top();
    q.pop();
    if (e.second == t) {
      Cout(e.first);
      return 0;
    }
    if (e.first > d[e.second])
      continue;
    for (int i : b[e.second]) {
      if (d[i] > d[e.second] + 1) {
        d[i] = d[e.second] + 1;
        q.emplace(d[i], i);
      }
    }
  }
  Cout(-1);
  // Couts(d);
}


Fixed submission:
#include <algorithm>
#include <cmath>
#include <iostream>
#include <numeric>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std;
using ll = long long;

void _cin() {}
template <class Head, class... Tail> void _cin(Head &&head, Tail &&...tail) {
  cin >> head;
  _cin(forward<Tail>(tail)...);
}
void _cout() { cout << "\n"; }
template <class Head, class... Tail> void _cout(Head &&head, Tail &&...tail) {
  cout << head;
  _cout(forward<Tail>(tail)...);
}
int gcd(int a, int b) { return (b == 0) ? a : gcd(b, a % b); }

#define Sq(x) (x) * (x)
#define For(i, n) for (int i = 0; i < (n); i++)
#define Rep(n) For(_, n)
#define Range(c) c.begin(), c.end()
#define RevRange(c) c.rbegin(), c.rend()
#define Contains(c, x) (find(Range(c), x) != c.end())
#define Search(rb, re, x) distance(rb, find(rb, re, x))
#define Sort(a) sort(Range(a))
#define DeSort(a) sort(RevRange(a))
#define Reverse(c) reverse(Range(c))
#define Unique(a) a.erase(unique(Range(a)), a.end())
#define Cusum(T, xs, sxs)                                                      \
  vector<T> sxs(xs.size() + 1);                                                \
  For(i, (int)xs.size()) sxs[i + 1] = sxs[i] + xs[i]
#define Cin(T, ...)                                                            \
  T __VA_ARGS__;                                                               \
  _cin(__VA_ARGS__)
#define Cins(T, n, xs)                                                         \
  vector<T> xs(n);                                                             \
  For(i, n) cin >> xs[i]
#define Cins2(T, n, xs, ys)                                                    \
  vector<T> xs(n), ys(n);                                                      \
  For(i, n) cin >> xs[i] >> ys[i]
#define Cins3(T, n, xs, ys, zs)                                                \
  vector<T> xs(n), ys(n), zs(n);                                               \
  For(i, n) cin >> xs[i] >> ys[i] >> zs[i]
#define Cinss(T, n, m, xs)                                                     \
  Vec2(T, n, m, xs);                                                           \
  For(i, n) For(j, m) cin >> xs[i][j]
#define Cinm(T, n, map)                                                        \
  unordered_map<T, int> map;                                                   \
  Rep(n) {                                                                     \
    Cin(T, x);                                                                 \
    map[x]++;                                                                  \
  }
#define Cout(...) _cout(__VA_ARGS__)
#define Couts(xs)                                                              \
  {                                                                            \
    for (const auto &e : xs)                                                   \
      cout << e << " ";                                                        \
    cout << "\n";                                                              \
  }
#define Coutyn(cond) Cout((cond) ? "yes" : "no")
#define CoutYn(cond) Cout((cond) ? "Yes" : "No")
#define CoutYN(cond) Cout((cond) ? "YES" : "NO")
#define vc vector
#define Mini(a, x) a = min(a, x)
#define Maxi(a, x) a = max(a, x)

// constexpr int MOD = 1e9+7;
#include <queue>

int main(void) {
  Cin(int, n, m);
  vc<vc<int>> a(n, vc<int>()), b(n, vc<int>());
  Rep(m) {
    Cin(int, u, v);
    u--, v--;
    a[u].push_back(v);
  }
  Cin(int, s, t);
  s--, t--;

  auto f = [&](vc<int> v) {
    vc<int> r;
    vc<bool> e(n);
    for (int i : v)
      for (int j : a[i]) {
        if (!e[j])
          e[j] = true, r.push_back(j);
      }
    return r;
  };

  {
    b[s] = f(f(f({s})));
    if (Contains(b[s], t)) {
      Cout(1);
      return 0;
    }
  }

  For(i, n) b[i] = f(f(f({i})));

  constexpr int Inf = 2e9;
  vc<int> d(n, Inf);
  d[s] = 0;

  using P = pair<int, int>;
  priority_queue<P, vector<P>, greater<P>> q;
  q.emplace(0, s);
  while (!q.empty()) {
    auto e = q.top();
    q.pop();
    if (e.second == t) {
      Cout(e.first);
      return 0;
    }
    if (e.first > d[e.second])
      continue;
    for (int i : b[e.second]) {
      if (d[i] > d[e.second] + 1) {
        d[i] = d[e.second] + 1;
        q.emplace(d[i], i);
      }
    }
  }
  Cout(-1);
  // Couts(d);
}