Problem p02573 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, ll> pil;
typedef pair<ll, int> pli;
typedef pair<double, double> pdd;
#define SQ(i) ((i) * (i))
#define MEM(a, b) memset(a, (b), sizeof(a))
#define SZ(i) int(i.size())
#define FOR(i, j, k, in) for (int i = j; i < (k); i += in)
#define RFOR(i, j, k, in) for (int i = j; i >= (k); i -= in)
#define REP(i, j) FOR(i, 0, j, 1)
#define REP1(i, j) FOR(i, 1, j + 1, 1)
#define RREP(i, j) RFOR(i, j, 0, 1)
#define ALL(_a) _a.begin(), _a.end()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define X first
#define Y second
#ifdef jayinnn
#define TIME(i) Timer i(#i)
#define debug(...)                                                             \\
  do {                                                                         \\
    fprintf(stderr, "%s - %d (%s) = ", __PRETTY_FUNCTION__, __LINE__,          \\
            #__VA_ARGS__);                                                     \\
    _do(__VA_ARGS__);                                                          \\
  } while (0)
template <typename T> void _do(T &&_x) { cerr << _x << endl; }
template <typename T, typename... S> void _do(T &&_x, S &&..._t) {
  cerr << _x << ", ";
  _do(_t...);
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, const pair<_a, _b> &_p) {
  return _s << "(" << _p.X << "," << _p.Y << ")";
}
template <typename It> ostream &_OUTC(ostream &_s, It _ita, It _itb) {
  _s << "{";
  for (It _it = _ita; _it != _itb; _it++) {
    _s << (_it == _ita ? "" : ",") << *_it;
  }
  _s << "}";
  return _s;
}
template <typename _a> ostream &operator<<(ostream &_s, vector<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a> ostream &operator<<(ostream &_s, set<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a> ostream &operator<<(ostream &_s, deque<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, map<_a, _b> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _t> void pary(_t _a, _t _b) {
  _OUTC(cerr, _a, _b);
  cerr << endl;
}
#define IOS()
class Timer {
private:
  string scope_name;
  chrono::high_resolution_clock::time_point start_time;

public:
  Timer(string name) : scope_name(name) {
    start_time = chrono::high_resolution_clock::now();
  }
  ~Timer() {
    auto stop_time = chrono::high_resolution_clock::now();
    auto length =
        chrono::duration_cast<chrono::microseconds>(stop_time - start_time)
            .count();
    double mlength = double(length) * 0.001;
    debug(scope_name, mlength);
  }
};
#else
#define TIME(i)
#define debug(...)
#define pary(...)
#define endl '\\n'
#define IOS()                                                                  \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0)
#endif

const ll MOD = 1000000007;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int iNF = 0x3f3f3f3f;
const ll MAXN = 100005;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

vector<vector<int>> adj;
vector<bool> vis;
int cnt;
void dfs(int src) {
  cnt++;
  for (auto i : adj[src]) {
    if (!vis[i]) {
      vis[i] = true;
      dfs(i);
    }
  }
}

/********** Good Luck :) **********/
int main() {
  TIME(main);
  IOS();
  int n, m;
  cin >> n >> m;
  adj.resize(n + 1);
  vis.resize(n + 1, false);
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    adj[a].pb(b);
    adj[b].pb(a);
  }

  int ans = 0;
  for (int i = 1; i <= n; i++) {
    if (!vis[i]) {
      vis[i] = true;
      cnt = 0;
      dfs(i);
      ans = max(ans, cnt);
    }
  }

  cout << ans << endl;

  return 0;
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, ll> pil;
typedef pair<ll, int> pli;
typedef pair<double, double> pdd;
#define SQ(i) ((i) * (i))
#define MEM(a, b) memset(a, (b), sizeof(a))
#define SZ(i) int(i.size())
#define FOR(i, j, k, in) for (int i = j; i < (k); i += in)
#define RFOR(i, j, k, in) for (int i = j; i >= (k); i -= in)
#define REP(i, j) FOR(i, 0, j, 1)
#define REP1(i, j) FOR(i, 1, j + 1, 1)
#define RREP(i, j) RFOR(i, j, 0, 1)
#define ALL(_a) _a.begin(), _a.end()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define X first
#define Y second
#ifdef jayinnn
#define TIME(i) Timer i(#i)
#define debug(...)                                                             \\
  do {                                                                         \\
    fprintf(stderr, "%s - %d (%s) = ", __PRETTY_FUNCTION__, __LINE__,          \\
            #__VA_ARGS__);                                                     \\
    _do(__VA_ARGS__);                                                          \\
  } while (0)
template <typename T> void _do(T &&_x) { cerr << _x << endl; }
template <typename T, typename... S> void _do(T &&_x, S &&..._t) {
  cerr << _x << ", ";
  _do(_t...);
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, const pair<_a, _b> &_p) {
  return _s << "(" << _p.X << "," << _p.Y << ")";
}
template <typename It> ostream &_OUTC(ostream &_s, It _ita, It _itb) {
  _s << "{";
  for (It _it = _ita; _it != _itb; _it++) {
    _s << (_it == _ita ? "" : ",") << *_it;
  }
  _s << "}";
  return _s;
}
template <typename _a> ostream &operator<<(ostream &_s, vector<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a> ostream &operator<<(ostream &_s, set<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a> ostream &operator<<(ostream &_s, deque<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, map<_a, _b> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _t> void pary(_t _a, _t _b) {
  _OUTC(cerr, _a, _b);
  cerr << endl;
}
#define IOS()
class Timer {
private:
  string scope_name;
  chrono::high_resolution_clock::time_point start_time;

public:
  Timer(string name) : scope_name(name) {
    start_time = chrono::high_resolution_clock::now();
  }
  ~Timer() {
    auto stop_time = chrono::high_resolution_clock::now();
    auto length =
        chrono::duration_cast<chrono::microseconds>(stop_time - start_time)
            .count();
    double mlength = double(length) * 0.001;
    debug(scope_name, mlength);
  }
};
#else
#define TIME(i)
#define debug(...)
#define pary(...)
#define endl '\\n'
#define IOS()                                                                  \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0)
#endif

const ll MOD = 1000000007;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int iNF = 0x3f3f3f3f;
const ll MAXN = 100005;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

/********** Good Luck :) **********/
int main() {
  TIME(main);
  IOS();
  int n, m;
  cin >> n >> m;
  vector<int> cnt(n + 2, 0);
  vector<vector<bool>> c(n + 2, vector<bool>(n + 2, false));
  int a, b;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    if (c[a][b] == false) {
      cnt[a]++;
      cnt[b]++;
      c[a][b] = true;
      c[b][a] = true;
    }
  }
  int ans = 0;
  REP(i, n + 1) ans = max(ans, cnt[i]);
  cout << ans + 1 << endl;

  return 0;
}