Problem p03805 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using vl = vector<ll>;
using vll = vector<vl>;
using vpll = vector<pll>;
using vs = vector<string>;
using tll = tuple<ll, ll, ll>;
using vtll = vector<tll>;
const ld PI = 3.1415926535897932;
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define rep1(n) for (ll i = 0; i < n; ++i)
#define rep2(i, n) for (ll i = 0; i < n; ++i)
#define rep3(i, a, b) for (ll i = a; i < b; ++i)
#define rep4(i, a, b, c) for (ll i = a; i < b; i += c)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define mp make_pair
#define mt make_tuple
void in() {}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail> void debug_out(Head h, Tail... t) {
  cerr << " " << h;
  if (sizeof...(t) > 0)
    cerr << " :";
  debug_out(t...);
}
template <typename T> ostream &operator<<(ostream &os, vector<T> vec) {
  for (size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
ll ctoi(char c) {
  switch (c) {
  case '0':
    return 0;
  case '1':
    return 1;
  case '2':
    return 2;
  case '3':
    return 3;
  case '4':
    return 4;
  case '5':
    return 5;
  case '6':
    return 6;
  case '7':
    return 7;
  case '8':
    return 8;
  case '9':
    return 9;
  default:
    return 0;
  }
}
bool pairCompare(const pll firstElof, pll secondElof) {
  return firstElof.first > secondElof.first;
}
//**Snippetリスト**//
// rep, vin, all, iteLoop, bitSearch, bitList, nod//
// gcdlcm, isPrime, eratos, primeFactorize, Npow, combination, divisor, modinv,
// digitDP// dfs, bfs, dijkstra, WarshallFloyd, BellmanFord, UnionFind, Kruskal
// ,RMQ, LCA//
ll i, j, k, l;
ll N, M, K, H, W, L, X, Y, Z, R, Q;
ll MOD = 1000000007;
ll INF = 1LL << 60;
ll ans = 0;
ll z = 0, o = 1;
vl flag;
vll path;
vl D;
//***********//
int main() {
  cin >> N >> M;
  vll path(N, vl(N, 0));
  for (i = 0; i < N; i++) {
    ll a, b;
    cin >> a >> b;
    a--;
    b--;
    path[a][b] = 1;
    path[b][a] = 1;
  }
  vl A(N);
  iota(A.begin(), A.end(), 0);
  do {
    if (A[0] == 0) {
      ll valid = 1;
      // debug(A);
      for (i = 0; i < N - 1; i++) {
        if (!path[A[i]][A[i + 1]])
          valid = 0;
      }
      ans += valid;
    }
  } while (next_permutation(A.begin(), A.end()));
  cout << ans;
}


Fixed submission:
#include <algorithm>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using vl = vector<ll>;
using vll = vector<vl>;
using vpll = vector<pll>;
using vs = vector<string>;
using tll = tuple<ll, ll, ll>;
using vtll = vector<tll>;
const ld PI = 3.1415926535897932;
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define rep1(n) for (ll i = 0; i < n; ++i)
#define rep2(i, n) for (ll i = 0; i < n; ++i)
#define rep3(i, a, b) for (ll i = a; i < b; ++i)
#define rep4(i, a, b, c) for (ll i = a; i < b; i += c)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define mp make_pair
#define mt make_tuple
void in() {}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail> void debug_out(Head h, Tail... t) {
  cerr << " " << h;
  if (sizeof...(t) > 0)
    cerr << " :";
  debug_out(t...);
}
template <typename T> ostream &operator<<(ostream &os, vector<T> vec) {
  for (size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
ll ctoi(char c) {
  switch (c) {
  case '0':
    return 0;
  case '1':
    return 1;
  case '2':
    return 2;
  case '3':
    return 3;
  case '4':
    return 4;
  case '5':
    return 5;
  case '6':
    return 6;
  case '7':
    return 7;
  case '8':
    return 8;
  case '9':
    return 9;
  default:
    return 0;
  }
}
bool pairCompare(const pll firstElof, pll secondElof) {
  return firstElof.first > secondElof.first;
}
//**Snippetリスト**//
// rep, vin, all, iteLoop, bitSearch, bitList, nod//
// gcdlcm, isPrime, eratos, primeFactorize, Npow, combination, divisor, modinv,
// digitDP// dfs, bfs, dijkstra, WarshallFloyd, BellmanFord, UnionFind, Kruskal
// ,RMQ, LCA//
ll i, j, k, l;
ll N, M, K, H, W, L, X, Y, Z, R, Q;
ll MOD = 1000000007;
ll INF = 1LL << 60;
ll ans = 0;
ll z = 0, o = 1;
vl flag;
vll path;
vl D;
//***********//
int main() {
  cin >> N >> M;
  vll path(N, vl(N, 0));
  for (i = 0; i < M; i++) {
    ll a, b;
    cin >> a >> b;
    a--;
    b--;
    path[a][b] = 1;
    path[b][a] = 1;
  }
  vl A(N);
  iota(A.begin(), A.end(), 0);
  do {
    if (A[0] == 0) {
      ll valid = 1;
      // debug(A);
      for (i = 0; i < N - 1; i++) {
        if (!path[A[i]][A[i + 1]])
          valid = 0;
      }
      ans += valid;
    }
  } while (next_permutation(A.begin(), A.end()));
  cout << ans;
}