Problem p03174 (C++)

Buggy submission (status: Time Limit Exceeded):
/*
これを入れて実行
g++ code.cpp
./a.out
 */

#include <algorithm>
#include <bitset>
#include <cmath>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stdio.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>

using namespace std;
typedef long long ll;
typedef long double ld;

int dy4[4] = {-1, 0, +1, 0};
int dx4[4] = {0, +1, 0, -1};
int dy8[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
int dx8[8] = {0, 1, 1, 1, 0, -1, -1, -1};

const long long INF = 1LL << 60;
const ll MOD = 1e9 + 7;

bool greaterSecond(const pair<int, int> &f, const pair<int, int> &s) {
  return f.second > s.second;
}

ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

ll nCr(ll n, ll r) {
  if (r == 0 || r == n) {
    return 1;
  } else if (r == 1) {
    return n;
  }
  return (nCr(n - 1, r) + nCr(n - 1, r - 1));
}

ll nPr(ll n, ll r) {
  r = n - r;
  ll ret = 1;
  for (ll i = n; i >= r + 1; i--)
    ret *= i;
  return ret;
}

//-----------------------ここから-----------
int n;
vector<vector<int>> a;
ll dp[23][(1LL << 23LL)];

int main(void) {
  cin >> n;
  a.resize(n);
  for (int i = 0; i < n; i++) {
    a[i].resize(n);
    for (int j = 0; j < n; j++) {
      cin >> a[i][j];
    }
  }

  dp[0][0] = 1;

  for (int i = 0; i < n; i++) {
    for (int bit = 0; bit < (1 << n); bit++) {
      for (int j = 0; j < n; j++) {
        if (!((1 << j) & bit) && a[i][j]) {
          dp[i + 1][bit | (1 << j)] += dp[i][bit];
          dp[i + 1][bit | (1 << j)] %= MOD;
        }
      }
    }
  }
  cout << dp[n][(1 << n) - 1] % MOD << endl;
}

Fixed submission:
/*
これを入れて実行
g++ code.cpp
./a.out
 */

#include <algorithm>
#include <bitset>
#include <cmath>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stdio.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>

using namespace std;
typedef long long ll;
typedef long double ld;

int dy4[4] = {-1, 0, +1, 0};
int dx4[4] = {0, +1, 0, -1};
int dy8[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
int dx8[8] = {0, 1, 1, 1, 0, -1, -1, -1};

const long long INF = 1LL << 60;
const ll MOD = 1e9 + 7;

bool greaterSecond(const pair<int, int> &f, const pair<int, int> &s) {
  return f.second > s.second;
}

ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

ll nCr(ll n, ll r) {
  if (r == 0 || r == n) {
    return 1;
  } else if (r == 1) {
    return n;
  }
  return (nCr(n - 1, r) + nCr(n - 1, r - 1));
}

ll nPr(ll n, ll r) {
  r = n - r;
  ll ret = 1;
  for (ll i = n; i >= r + 1; i--)
    ret *= i;
  return ret;
}

//-----------------------ここから-----------
int n;
vector<vector<int>> a;
ll dp[23][(1LL << 23LL)];

int main(void) {
  cin >> n;
  a.resize(n);
  for (int i = 0; i < n; i++) {
    a[i].resize(n);
    for (int j = 0; j < n; j++) {
      cin >> a[i][j];
    }
  }

  dp[0][0] = 1;

  for (int i = 0; i < n; i++) {
    for (int bit = 0; bit < (1 << n); bit++) {
      if (dp[i][bit] == 0)
        continue;
      for (int j = 0; j < n; j++) {
        if (!((1 << j) & bit) && a[i][j]) {
          dp[i + 1][bit | (1 << j)] += dp[i][bit];
          dp[i + 1][bit | (1 << j)] %= MOD;
        }
      }
    }
  }
  cout << dp[n][(1 << n) - 1] % MOD << endl;
}