Problem p03174 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#define M_PI 3.14159265358979323846

using namespace std;

// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
inline int readInt() {
  int x;
  scanf("%d", &x);
  return x;
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

// container util

//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a) * (a))
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define MOD 1000000007

const int N = 1 << 21;
LL dp[21][N];
int a[21][21];
int main() {
  int n;
  scanf("%d", &n);
  REP(i, n) REP(j, n) scanf("%d", &a[i][j]);
  dp[0][0] = 1;
  REP(i, n) {
    REP(k, 1 << n) {
      if (!dp[i][k])
        continue;
      REP(j, n) {
        if (!a[i][j])
          continue;
        if (k & (1 << j))
          continue;
        dp[i + 1][k | (1 << j)] = (dp[i + 1][k | (1 << j)] + dp[i][k]) % MOD;
      }
    }
  }
  cout << dp[n][(1 << n) - 1] << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#define M_PI 3.14159265358979323846

using namespace std;

// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
inline int readInt() {
  int x;
  scanf("%d", &x);
  return x;
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

// container util

//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a) * (a))
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define MOD 1000000007

const int N = 1 << 21;
LL dp[22][N];
int a[21][21];
int main() {
  int n;
  scanf("%d", &n);
  REP(i, n) REP(j, n) scanf("%d", &a[i][j]);
  dp[0][0] = 1;
  REP(i, n) {
    REP(k, 1 << n) {
      if (!dp[i][k])
        continue;
      REP(j, n) {
        if (!a[i][j])
          continue;
        if (k & (1 << j))
          continue;
        dp[i + 1][k | (1 << j)] = (dp[i + 1][k | (1 << j)] + dp[i][k]) % MOD;
      }
    }
  }
  cout << dp[n][(1 << n) - 1] << endl;
  return 0;
}