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

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double lf;
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
#define REP(i, n) for (int i = 0; i < n; i++)
#define REP1(i, n) for (int i = 1; i <= n; i++)
#define RST(i, n) memset(i, n, sizeof i)
#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define X first
#define Y second
#define eb emplace_back
#ifdef cold66
#define debug(...)                                                             \\
  do {                                                                         \\
    fprintf(stderr, "LINE %d: (%s) = ", __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, 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()
#else
#define debug(...)
#define pary(...)
#define endl '\\n'
#define IOS()                                                                  \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);
#endif // cold66
//}
template <class T> inline bool chkmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chkmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}

const ll MAXn = 2e5 + 5, MAXlg = __lg(MAXn) + 2;
const ll MOD = 1000000007;
const ll INF = 0x3f3f3f3f;

int ans = 1;
int dsu[MAXn], sz[MAXn];
int fnd(int x) {
  if (dsu[x] == x)
    return x;
  return dsu[x] = fnd(dsu[x]);
}
void mrg(int x, int y) {
  x = fnd(x), y = fnd(y);
  if (x == y)
    return;
  if (sz[x] < sz[y])
    swap(x, y);
  dsu[y] = x;
  sz[x] += sz[y];
  ans = max(ans, sz[x]);
}
int main() {
  IOS();
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; ++i) {
    dsu[i] = i, sz[i] = 1;
  }
  for (int i = 0; i < m; ++i) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    mrg(u, v);
  }
  cout << ans << endl;
}


Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double lf;
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
#define REP(i, n) for (int i = 0; i < n; i++)
#define REP1(i, n) for (int i = 1; i <= n; i++)
#define RST(i, n) memset(i, n, sizeof i)
#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define X first
#define Y second
#define eb emplace_back
#ifdef cold66
#define debug(...)                                                             \\
  do {                                                                         \\
    fprintf(stderr, "LINE %d: (%s) = ", __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, 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()
#else
#define debug(...)
#define pary(...)
#define endl '\\n'
#define IOS()                                                                  \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);
#endif // cold66
//}
template <class T> inline bool chkmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chkmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}

const ll MAXn = 1e5 + 5, MAXlg = __lg(MAXn) + 2;
const ll MOD = 1000000007;
const ll INF = 0x3f3f3f3f;

int ans;
int dsu[MAXn], sz[MAXn];
int fnd(int x) {
  if (dsu[x] == x)
    return x;
  return dsu[x] = fnd(dsu[x]);
}
void mrg(int x, int y) {
  x = fnd(x), y = fnd(y);
  if (x == y)
    return;
  if (sz[x] < sz[y])
    swap(x, y);
  dsu[y] = x;
  sz[x] += sz[y];
  ans = max(ans, sz[x]);
}
int main() {
  IOS();
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; ++i) {
    dsu[i] = i, sz[i] = 1;
  }
  for (int i = 0; i < m; ++i) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    mrg(u, v);
  }
  cout << ans << endl;
}