Problem p03805 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

void Init() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  struct Init_caller {
    Init_caller() { Init(); }
  } caller;
}

#define int LL
#define rep(i, n) for (LL(i) = 0; (i) < (n); (i)++)
#define all(a) (a).begin(), (a).end()
#define size(s) ((LL)s.size())
#define F first
#define S second
#define check() cout << "! ! !"
#define endl "\n"
#define _y() cout << "Yes" << endl
#define _Y() cout << "YES" << endl
#define _n() cout << "No" << endl
#define _N() cout << "NO" << endl
#define INT_INF INT_MAX
#define INF LLONG_MAX
#define MOD ((int)pow(10, 9) + 7)

using namespace std;

using LL = long long;
using st = string;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<st>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using qi = queue<int>;
using qc = queue<char>;
using qs = queue<st>;
using si = stack<int>;
using sc = stack<char>;
using ss = stack<st>;
using pi = pair<int, int>;
using ppi = pair<pi, int>;
using mii = map<int, int>;
using mpii = map<pi, int>;
using mib = map<int, bool>;
using mci = map<char, int>;
using msb = map<st, bool>;
using vpi = vector<pi>;
using vppi = vector<ppi>;
using spi = stack<pi>;
using qpi = queue<pi>;

// 4,2,8,6,1,7,3,9,5
int dx[] = {-1, 0, 0, 1, -1, -1, 1, 1, 0};
int dy[] = {0, 1, -1, 0, 1, -1, 1, -1, 0};

istream &operator>>(istream &in, vi &v) {
  rep(i, size(v)) { in >> v[i]; }
  return in;
}

ostream &operator<<(ostream &out, vi &v) {
  rep(i, size(v)) { out << "v[" << i << "] = " << v[i] << endl; }
  return out;
}

void y_n(bool p) { p ? _y() : _n(); }

void Y_N(bool p) { p ? _Y() : _N(); }

LL vmax(vi v) {
  int n = size(v);
  int MAX = 0;
  rep(i, n) { MAX = max(MAX, v[i]); }
  return MAX;
}

LL vmin(vi v) {
  int n = size(v);
  int MIN = INF;
  rep(i, n) { MIN = min(MIN, v[i]); }
  return MIN;
}

LL vsum(vi v) {
  int n = size(v);
  int sum = 0;
  rep(i, n) { sum += v[i]; }
  return sum;
}

LL gcd(LL a, LL b) {
  if (b == 0) {
    swap(a, b);
  }
  LL r;
  while ((r = a % b) != 0) {
    a = b;
    b = r;
  }
  return b;
}
LL lcm(LL a, LL b) { return (a / gcd(a, b) * b); }

bool is_square(int n) {
  if ((int)sqrt(n) * (int)sqrt(n) == n) {
    return true;
  } else {
    return false;
  }
}

bool is_prime(int n) {
  if (n == 1) {
    return false;
  } else {
    for (int i = 2; i * i <= n; i++) {
      if (n % i == 0) {
        return false;
      }
    }
  }
  return true;
}

void dec_num(int n, vi &v) {
  int a = 2;
  v.push_back(1);
  v.push_back(n);
  while (a * a <= n) {
    if (n % a == 0) {
      v.push_back(a);
      v.push_back(n / a);
    }
    a++;
  }
  sort(all(v));
}

void dec_prime(int n, vi &v) {
  v.push_back(1);
  int a = 2;
  while (a * a <= n) {
    if (n % a == 0) {
      v.push_back(a);
      n /= a;
    } else {
      a++;
    }
  }
  v.push_back(n);
}

int sieve_prime(LL a, LL b) {
  if (a > b)
    swap(a, b);
  vb s(b + 1, true);
  int cnt_a = 0, cnt_b = 0;
  for (int i = 2; i <= b; i++) {
    for (int j = 2; i * j <= b; j++) {
      s[i * j] = false;
    }
  }
  for (int i = 2; i <= b; i++) {
    if (s[i]) {
      // cout << i << " ";
      if (i < a) {
        cnt_a++;
      }
      cnt_b++;
    }
  }
  return cnt_b - cnt_a;
}

LL factorial(LL n) {
  LL a = 1, ret = 1;
  while (a < n) {
    a++;
    ret *= a;
    // ret %= MOD;
  }
  return ret;
}

const int COMBMAX = 4000;
int comb[COMBMAX + 5][COMBMAX + 5];

void init_comb() {
  comb[0][0] = 1;
  rep(i, COMBMAX) {
    rep(j, i + 1) {
      comb[i + 1][j] += comb[i][j];
      comb[i + 1][j] %= MOD;
      comb[i + 1][j + 1] += comb[i][j];
      comb[i + 1][j + 1] %= MOD;
    }
  }
}

int combination(int n, int k) {
  if (k < 0 || k > n)
    return 0;
  else
    return comb[n][k];
}

const int COMBMODMAX = 510000;
int fac[COMBMODMAX], facinv[COMBMODMAX], inv[COMBMODMAX];

void init_comb_mod() {
  fac[0] = fac[1] = 1;
  facinv[0] = facinv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < COMBMODMAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    facinv[i] = facinv[i - 1] * inv[i] % MOD;
  }
}

int comb_mod(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (facinv[k] * facinv[n - k] % MOD) % MOD;
}

int pow_mod(int x, int n, int p) {
  if (n == 0)
    return 0;
  int res = pow_mod(x * x % p, n / 2, p);
  if (n % 2 == 1)
    res = res * x % p;
  return res;
}

class UF {
public:
  vi par;
  vi rank;

  UF(int n) {
    par.resize(n, -1);
    rank.resize(n, 0);
  }

  int root(int x) {
    if (par[x] == -1)
      return x;
    return par[x] = root(par[x]);
  }

  // xの集合の位数
  int order(int x) { return -par[root(x)]; }

  // xとyを併合
  void unite(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y) {
      return;
    }

    if (rank[x] < rank[y]) {
      par[x] = y;
    } else {
      par[y] = x;
      if (rank[x] == rank[y])
        rank[x]++;
    }
  }

  // xとyが同じ集合にあるか
  bool is_same(int x, int y) { return root(x) == root(y); }
};

struct edge {
  int to;
  int cost;
};

using ve = vector<edge>;
using vve = vector<ve>;

/*****************************************************************************/
signed main() {

  int n, m;
  cin >> n >> m;
  vvb g(m, vb(m, false));
  rep(i, m) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    g[a][b] = g[b][a] = true;
  }
  vi v;
  rep(i, n) { v.push_back(i); }
  int ans = 0;
  rep(i, factorial(n - 1)) {
    bool f = true;
    rep(i, size(v) - 1) {
      if (!g[v[i]][v[i + 1]])
        f = false;
    }
    if (f)
      ans++;
    // cout << v;
    next_permutation(all(v));
  }
  cout << ans;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

void Init() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  struct Init_caller {
    Init_caller() { Init(); }
  } caller;
}

#define int LL
#define rep(i, n) for (LL(i) = 0; (i) < (n); (i)++)
#define all(a) (a).begin(), (a).end()
#define size(s) ((LL)s.size())
#define F first
#define S second
#define check() cout << "! ! !"
#define endl "\n"
#define _y() cout << "Yes" << endl
#define _Y() cout << "YES" << endl
#define _n() cout << "No" << endl
#define _N() cout << "NO" << endl
#define INT_INF INT_MAX
#define INF LLONG_MAX
#define MOD ((int)pow(10, 9) + 7)

using namespace std;

using LL = long long;
using st = string;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<st>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using qi = queue<int>;
using qc = queue<char>;
using qs = queue<st>;
using si = stack<int>;
using sc = stack<char>;
using ss = stack<st>;
using pi = pair<int, int>;
using ppi = pair<pi, int>;
using mii = map<int, int>;
using mpii = map<pi, int>;
using mib = map<int, bool>;
using mci = map<char, int>;
using msb = map<st, bool>;
using vpi = vector<pi>;
using vppi = vector<ppi>;
using spi = stack<pi>;
using qpi = queue<pi>;

// 4,2,8,6,1,7,3,9,5
int dx[] = {-1, 0, 0, 1, -1, -1, 1, 1, 0};
int dy[] = {0, 1, -1, 0, 1, -1, 1, -1, 0};

istream &operator>>(istream &in, vi &v) {
  rep(i, size(v)) { in >> v[i]; }
  return in;
}

ostream &operator<<(ostream &out, vi &v) {
  rep(i, size(v)) { out << "v[" << i << "] = " << v[i] << endl; }
  return out;
}

void y_n(bool p) { p ? _y() : _n(); }

void Y_N(bool p) { p ? _Y() : _N(); }

LL vmax(vi v) {
  int n = size(v);
  int MAX = 0;
  rep(i, n) { MAX = max(MAX, v[i]); }
  return MAX;
}

LL vmin(vi v) {
  int n = size(v);
  int MIN = INF;
  rep(i, n) { MIN = min(MIN, v[i]); }
  return MIN;
}

LL vsum(vi v) {
  int n = size(v);
  int sum = 0;
  rep(i, n) { sum += v[i]; }
  return sum;
}

LL gcd(LL a, LL b) {
  if (b == 0) {
    swap(a, b);
  }
  LL r;
  while ((r = a % b) != 0) {
    a = b;
    b = r;
  }
  return b;
}
LL lcm(LL a, LL b) { return (a / gcd(a, b) * b); }

bool is_square(int n) {
  if ((int)sqrt(n) * (int)sqrt(n) == n) {
    return true;
  } else {
    return false;
  }
}

bool is_prime(int n) {
  if (n == 1) {
    return false;
  } else {
    for (int i = 2; i * i <= n; i++) {
      if (n % i == 0) {
        return false;
      }
    }
  }
  return true;
}

void dec_num(int n, vi &v) {
  int a = 2;
  v.push_back(1);
  v.push_back(n);
  while (a * a <= n) {
    if (n % a == 0) {
      v.push_back(a);
      v.push_back(n / a);
    }
    a++;
  }
  sort(all(v));
}

void dec_prime(int n, vi &v) {
  v.push_back(1);
  int a = 2;
  while (a * a <= n) {
    if (n % a == 0) {
      v.push_back(a);
      n /= a;
    } else {
      a++;
    }
  }
  v.push_back(n);
}

int sieve_prime(LL a, LL b) {
  if (a > b)
    swap(a, b);
  vb s(b + 1, true);
  int cnt_a = 0, cnt_b = 0;
  for (int i = 2; i <= b; i++) {
    for (int j = 2; i * j <= b; j++) {
      s[i * j] = false;
    }
  }
  for (int i = 2; i <= b; i++) {
    if (s[i]) {
      // cout << i << " ";
      if (i < a) {
        cnt_a++;
      }
      cnt_b++;
    }
  }
  return cnt_b - cnt_a;
}

LL factorial(LL n) {
  LL a = 1, ret = 1;
  while (a < n) {
    a++;
    ret *= a;
    // ret %= MOD;
  }
  return ret;
}

const int COMBMAX = 4000;
int comb[COMBMAX + 5][COMBMAX + 5];

void init_comb() {
  comb[0][0] = 1;
  rep(i, COMBMAX) {
    rep(j, i + 1) {
      comb[i + 1][j] += comb[i][j];
      comb[i + 1][j] %= MOD;
      comb[i + 1][j + 1] += comb[i][j];
      comb[i + 1][j + 1] %= MOD;
    }
  }
}

int combination(int n, int k) {
  if (k < 0 || k > n)
    return 0;
  else
    return comb[n][k];
}

const int COMBMODMAX = 510000;
int fac[COMBMODMAX], facinv[COMBMODMAX], inv[COMBMODMAX];

void init_comb_mod() {
  fac[0] = fac[1] = 1;
  facinv[0] = facinv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < COMBMODMAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    facinv[i] = facinv[i - 1] * inv[i] % MOD;
  }
}

int comb_mod(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (facinv[k] * facinv[n - k] % MOD) % MOD;
}

int pow_mod(int x, int n, int p) {
  if (n == 0)
    return 0;
  int res = pow_mod(x * x % p, n / 2, p);
  if (n % 2 == 1)
    res = res * x % p;
  return res;
}

class UF {
public:
  vi par;
  vi rank;

  UF(int n) {
    par.resize(n, -1);
    rank.resize(n, 0);
  }

  int root(int x) {
    if (par[x] == -1)
      return x;
    return par[x] = root(par[x]);
  }

  // xの集合の位数
  int order(int x) { return -par[root(x)]; }

  // xとyを併合
  void unite(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y) {
      return;
    }

    if (rank[x] < rank[y]) {
      par[x] = y;
    } else {
      par[y] = x;
      if (rank[x] == rank[y])
        rank[x]++;
    }
  }

  // xとyが同じ集合にあるか
  bool is_same(int x, int y) { return root(x) == root(y); }
};

struct edge {
  int to;
  int cost;
};

using ve = vector<edge>;
using vve = vector<ve>;

/*****************************************************************************/
signed main() {

  int n, m;
  cin >> n >> m;
  vvb g(n, vb(n, false));
  rep(i, m) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    g[a][b] = g[b][a] = true;
  }
  vi v;
  rep(i, n) { v.push_back(i); }
  int ans = 0;
  rep(i, factorial(n - 1)) {
    bool f = true;
    rep(i, size(v) - 1) {
      if (!g[v[i]][v[i + 1]])
        f = false;
    }
    if (f)
      ans++;
    // cout << v;
    next_permutation(all(v));
  }
  cout << ans;
  return 0;
}