Problem p03174 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;

using i64 = int64_t;

#define rep(i, x, y)                                                           \
  for (i64 i = i64(x), i##_max_for_repmacro = i64(y);                          \
       i < i##_max_for_repmacro; ++i)
#define debug(x) #x << "=" << (x)

#ifdef DEBUG
#define _GLIBCXX_DEBUG
#define print(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define print(x)
#endif

const int inf = 1.01e9;
const i64 inf64 = 4.01e18;
const double eps = 1e-9;

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "[";
  for (const auto &v : vec) {
    os << v << ",";
  }
  os << "]";
  return os;
}

template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

void solve() {
  const i64 mod = 1'000'000'007;
  i64 N;
  cin >> N;

  vector<vector<i64>> a(N, vector<i64>(N));
  rep(i, 0, N) {
    rep(j, 0, N) { cin >> a[i][j]; }
  }

  const i64 size = 21;
  static i64 dp[size][1 << size];
  fill_n((i64 *)dp, size * (1 << size), 0);

  rep(j, 0, N) {
    if (a[0][j] == 0)
      continue;
    ++dp[0][1 << j];
  }

  rep(i, 0, N - 1) {
    rep(s, 0, 1 << N) {
      rep(j, 0, N) {
        if (s & (1 << j))
          continue;
        if (a[i + 1][j] == 0)
          continue;
        i64 t = s | (1 << j);
        dp[i + 1][t] += dp[i][s];
        dp[i + 1][t] %= mod;
      }
    }
  }

  cout << dp[N - 1][(1 << N) - 1] << endl;
}

int main() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  cout.setf(ios::fixed);
  cout.precision(16);
  solve();
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

using i64 = int64_t;

#define rep(i, x, y)                                                           \
  for (i64 i = i64(x), i##_max_for_repmacro = i64(y);                          \
       i < i##_max_for_repmacro; ++i)
#define debug(x) #x << "=" << (x)

#ifdef DEBUG
#define _GLIBCXX_DEBUG
#define print(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define print(x)
#endif

const int inf = 1.01e9;
const i64 inf64 = 4.01e18;
const double eps = 1e-9;

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "[";
  for (const auto &v : vec) {
    os << v << ",";
  }
  os << "]";
  return os;
}

template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

void solve() {
  const i64 mod = 1'000'000'007;
  i64 N;
  cin >> N;

  vector<vector<i64>> a(N, vector<i64>(N));
  rep(i, 0, N) {
    rep(j, 0, N) { cin >> a[i][j]; }
  }

  const i64 size = 21;
  static i64 dp[size][1 << size];
  fill_n((i64 *)dp, size * (1 << size), 0);

  rep(j, 0, N) {
    if (a[0][j] == 0)
      continue;
    ++dp[0][1 << j];
  }

  rep(i, 0, N - 1) {
    rep(s, 0, 1 << N) {
      if (dp[i][s] == 0)
        continue;
      rep(j, 0, N) {
        if (s & (1 << j))
          continue;
        if (a[i + 1][j] == 0)
          continue;
        i64 t = s | (1 << j);
        dp[i + 1][t] += dp[i][s];
        dp[i + 1][t] %= mod;
      }
    }
  }

  cout << dp[N - 1][(1 << N) - 1] << endl;
}

int main() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  cout.setf(ios::fixed);
  cout.precision(16);
  solve();
  return 0;
}