Problem p03174 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> P;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
#define pb push_back
#define mp make_pair
#define eps 1e-9
#define INF 2000000000
#define LLINF 1000000000000000ll
#define sz(x) ((int)(x).size())
#define fi first
#define sec second
#define all(x) (x).begin(), (x).end()
#define sq(x) ((x) * (x))
#define rep(i, n) for (int(i) = 0; (i) < (int)(n); (i)++)
#define repn(i, a, n) for (int(i) = (a); (i) < (int)(n); (i)++)
#define EQ(a, b) (abs((a) - (b)) < eps)
#define dmp(x) cerr << __LINE__ << " " << #x << " " << x << endl;
template <class T> void chmin(T &a, const T &b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, const T &b) {
  if (a < b)
    a = b;
}
template <class T, class U> ostream &operator<<(ostream &os, pair<T, U> &p) {
  os << p.fi << ',' << p.sec;
  return os;
}
template <class T, class U> istream &operator>>(istream &is, pair<T, U> &p) {
  is >> p.fi >> p.sec;
  return is;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i];
    if (i + 1 < vec.size())
      os << ' ';
  }
  return os;
}
template <class T> istream &operator>>(istream &is, vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++)
    is >> vec[i];
  return is;
}
void fastio() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed << setprecision(20);
}
ll MOD = 1000000007ll; // if inv is needed, this shold be prime.
struct ModInt {
  ll val;
  ModInt() : val(0ll) {}
  ModInt(ll v) : val(((v % MOD) + MOD) % MOD) {}
  ModInt exp(ll y) const {
    if (!y)
      return ModInt(1ll);
    ModInt a = exp(y / 2ll);
    a *= a;
    if (y & 1)
      a *= (*this);
    return a;
  }
  bool operator==(const ModInt &x) const { return val == x.val; }
  inline bool operator!=(const ModInt &x) const { return !(*this == x); }
  bool operator<(const ModInt &x) const { return val < x.val; }
  bool operator>(const ModInt &x) const { return val > x.val; }
  inline bool operator>=(const ModInt &x) const { return !(*this < x); }
  inline bool operator<=(const ModInt &x) const { return !(*this > x); }
  ModInt &operator+=(const ModInt &x) {
    if ((val += x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt &x) {
    if ((val += MOD - x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt &x) {
    (val *= x.val) %= MOD;
    return *this;
  }
  ModInt operator+(const ModInt &x) const { return ModInt(*this) += x; }
  ModInt operator-(const ModInt &x) const { return ModInt(*this) -= x; }
  ModInt operator*(const ModInt &x) const { return ModInt(*this) *= x; }
};
istream &operator>>(istream &i, ModInt &x) {
  i >> x.val;
  return i;
}
ostream &operator<<(ostream &o, const ModInt &x) {
  o << x.val;
  return o;
}
ModInt pow(ModInt a, ll x) {
  ModInt res = ModInt(1ll);
  while (x) {
    if (x & 1)
      res *= a;
    x >>= 1;
    a = a * a;
  }
  return res;
}
const int SIZE = 100100;
ModInt inv[SIZE + 10], fac[SIZE + 10], facinv[SIZE + 10];
// notice: 0C0 = 1
ModInt nCr(int n, int r) {
  assert(!(n < r));
  assert(!(n < 0 || r < 0));
  return fac[n] * facinv[r] * facinv[n - r];
}
void init() {
  fac[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    fac[i] = fac[i - 1] * ModInt(i);
  inv[1] = ModInt(1ll);
  for (int i = 2; i <= SIZE; i++)
    inv[i] = ModInt(0ll) - ModInt(MOD / i) * inv[MOD % i];
  facinv[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    facinv[i] = facinv[i - 1] * inv[i];
  return;
}
int N;
int a[30][30];
ModInt dp[24][1 << 22];
int main() {
  cin >> N;
  rep(i, N) {
    rep(j, N) { cin >> a[i][j]; }
  }
  dp[0][0] = ModInt(1ll);
  rep(i, N) {
    rep(j, (1 << N)) {
      rep(k, N) {
        if (a[i][k] == 0)
          continue;
        if ((j >> k) & 1)
          continue;
        dp[i + 1][j | (1 << k)] += dp[i][j];
      }
    }
  }
  cout << dp[N][(1 << N) - 1] << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> P;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
#define pb push_back
#define mp make_pair
#define eps 1e-9
#define INF 2000000000
#define LLINF 1000000000000000ll
#define sz(x) ((int)(x).size())
#define fi first
#define sec second
#define all(x) (x).begin(), (x).end()
#define sq(x) ((x) * (x))
#define rep(i, n) for (int(i) = 0; (i) < (int)(n); (i)++)
#define repn(i, a, n) for (int(i) = (a); (i) < (int)(n); (i)++)
#define EQ(a, b) (abs((a) - (b)) < eps)
#define dmp(x) cerr << __LINE__ << " " << #x << " " << x << endl;
template <class T> void chmin(T &a, const T &b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, const T &b) {
  if (a < b)
    a = b;
}
template <class T, class U> ostream &operator<<(ostream &os, pair<T, U> &p) {
  os << p.fi << ',' << p.sec;
  return os;
}
template <class T, class U> istream &operator>>(istream &is, pair<T, U> &p) {
  is >> p.fi >> p.sec;
  return is;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i];
    if (i + 1 < vec.size())
      os << ' ';
  }
  return os;
}
template <class T> istream &operator>>(istream &is, vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++)
    is >> vec[i];
  return is;
}
void fastio() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed << setprecision(20);
}
ll MOD = 1000000007ll; // if inv is needed, this shold be prime.
struct ModInt {
  ll val;
  ModInt() : val(0ll) {}
  ModInt(ll v) : val(((v % MOD) + MOD) % MOD) {}
  ModInt exp(ll y) const {
    if (!y)
      return ModInt(1ll);
    ModInt a = exp(y / 2ll);
    a *= a;
    if (y & 1)
      a *= (*this);
    return a;
  }
  bool operator==(const ModInt &x) const { return val == x.val; }
  inline bool operator!=(const ModInt &x) const { return !(*this == x); }
  bool operator<(const ModInt &x) const { return val < x.val; }
  bool operator>(const ModInt &x) const { return val > x.val; }
  inline bool operator>=(const ModInt &x) const { return !(*this < x); }
  inline bool operator<=(const ModInt &x) const { return !(*this > x); }
  ModInt &operator+=(const ModInt &x) {
    if ((val += x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt &x) {
    if ((val += MOD - x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt &x) {
    (val *= x.val) %= MOD;
    return *this;
  }
  ModInt operator+(const ModInt &x) const { return ModInt(*this) += x; }
  ModInt operator-(const ModInt &x) const { return ModInt(*this) -= x; }
  ModInt operator*(const ModInt &x) const { return ModInt(*this) *= x; }
};
istream &operator>>(istream &i, ModInt &x) {
  i >> x.val;
  return i;
}
ostream &operator<<(ostream &o, const ModInt &x) {
  o << x.val;
  return o;
}
ModInt pow(ModInt a, ll x) {
  ModInt res = ModInt(1ll);
  while (x) {
    if (x & 1)
      res *= a;
    x >>= 1;
    a = a * a;
  }
  return res;
}
const int SIZE = 100100;
ModInt inv[SIZE + 10], fac[SIZE + 10], facinv[SIZE + 10];
// notice: 0C0 = 1
ModInt nCr(int n, int r) {
  assert(!(n < r));
  assert(!(n < 0 || r < 0));
  return fac[n] * facinv[r] * facinv[n - r];
}
void init() {
  fac[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    fac[i] = fac[i - 1] * ModInt(i);
  inv[1] = ModInt(1ll);
  for (int i = 2; i <= SIZE; i++)
    inv[i] = ModInt(0ll) - ModInt(MOD / i) * inv[MOD % i];
  facinv[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    facinv[i] = facinv[i - 1] * inv[i];
  return;
}
int N;
int a[30][30];
ModInt dp[24][1 << 22];
int main() {
  cin >> N;
  rep(i, N) {
    rep(j, N) { cin >> a[i][j]; }
  }
  dp[0][0] = ModInt(1ll);
  rep(i, N) {
    rep(j, (1 << N)) {
      if (__builtin_popcount(j) != i)
        continue;
      rep(k, N) {
        if (a[i][k] == 0)
          continue;
        if ((j >> k) & 1)
          continue;
        dp[i + 1][j | (1 << k)] += dp[i][j];
      }
    }
  }
  cout << dp[N][(1 << N) - 1] << endl;
  return 0;
}