Problem p02998 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#include <random>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
#define int ll
// #define int __int128
// #define ll __int128
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<short> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<ld> vld;
typedef vector<vld> vvld;
typedef vector<vvld> vvvld;
typedef vector<string> vst;
typedef vector<vst> vvst;
typedef pair<ld, ld> pld;
typedef complex<double> base;

#define inmin(a, b) a = min(a, (b))
#define inmax(a, b) a = max(a, (b))
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.rbegin(), a.rend()
#define sqr(x) ((x) * (x))
#define fori(i, n) for (int i = 0; i < int(n); ++i)
#define SZ(a) ((int)((a).size()))
#define triple(T) tuple<T, T, T>
#define quad(T) tuple<T, T, T, T>
#define watch(x) cerr << (#x) << " = " << (x) << endl;

const double PI = 2 * acos(0.0);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng_64(chrono::steady_clock::now().time_since_epoch().count());

const string DIGITS = "0123456789";
const string ALPH = "abcdefghijklmnopqrstuvwxyz";

template <class T0, class T1>
inline ostream &operator<<(ostream &out, pair<T0, T1> &a) {
  return out << "{" << a.first << ", " << a.second << "}";
}

template <class T0, class T1, class T2>
inline ostream &operator<<(ostream &out, tuple<T0, T1, T2> &a) {
  return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a)
             << "}";
}

template <class T0, class T1, class T2, class T3>
inline ostream &operator<<(ostream &out, tuple<T0, T1, T2, T3> &a) {
  return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a)
             << ", " << get<3>(a) << "}";
}

template <class T> inline ostream &operator<<(ostream &out, vector<T> &a) {
  out << "[";
  fori(i, a.size()) out << a[i]
                        << vector<string>{", ", "]  "}[i + 1 == a.size()];
  return out;
}

void smain();

signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);

#ifdef RUS_HOME
  freopen("input.txt", "r", stdin);
  clock_t start = clock();
#endif
  // freopen("input.txt", "r", stdin);
  // freopen("output.txt", "w", stdout);
  cout << setprecision(12) << fixed;
  smain();
#ifdef RUS_HOME
  cout << "\n\nTOTAL EXECUTION TIME: "
       << float(clock() - start) / CLOCKS_PER_SEC << endl;
#endif
}
const int oo = 1e9;
const int N = 1e5 + 100;
int MOD = 1e9 + 7;

vi gx[N], gy[N];
vi cur(N);
vi p[N];

void uni(int a, int b) {
  a = cur[a];
  b = cur[b];
  if (p[a].size() > p[b].size())
    swap(a, b);
  for (int i = 0; i < p[a].size(); i++) {
    p[b].push_back(p[a][i]);
    cur[p[a][i]] = b;
  }
  p[a].clear();
}

void smain() {

  int n;
  cin >> n;
  vi x(n), y(n);
  for (int i = 0; i < n; i++) {
    cin >> x[i] >> y[i];
    gx[x[i]].push_back(i);
    gy[y[i]].push_back(i);
    cur[i] = i;
    p[i].push_back(i);
  }

  for (int i = 0; i < N; i++) {
    for (int j = 1; j < gx[i].size(); j++) {
      uni(gx[i][j], gx[i][j - 1]);
    }
    for (int j = 1; j < gy[i].size(); j++) {
      uni(gy[i][j], gy[i][j - 1]);
    }
  }
  int ans = 0;
  for (int i = 0; i < N; i++) {
    set<int> sx, sy;
    for (int j = 0; j < p[i].size(); j++) {
      sx.insert(x[p[i][j]]);
      sy.insert(y[p[i][j]]);
    }
    ans += sx.size() * sy.size();
  }
  cout << ans - n;
}

Fixed submission:
#include <bits/stdc++.h>
#include <random>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
#define int ll
// #define int __int128
// #define ll __int128
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<short> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<ld> vld;
typedef vector<vld> vvld;
typedef vector<vvld> vvvld;
typedef vector<string> vst;
typedef vector<vst> vvst;
typedef pair<ld, ld> pld;
typedef complex<double> base;

#define inmin(a, b) a = min(a, (b))
#define inmax(a, b) a = max(a, (b))
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.rbegin(), a.rend()
#define sqr(x) ((x) * (x))
#define fori(i, n) for (int i = 0; i < int(n); ++i)
#define SZ(a) ((int)((a).size()))
#define triple(T) tuple<T, T, T>
#define quad(T) tuple<T, T, T, T>
#define watch(x) cerr << (#x) << " = " << (x) << endl;

const double PI = 2 * acos(0.0);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng_64(chrono::steady_clock::now().time_since_epoch().count());

const string DIGITS = "0123456789";
const string ALPH = "abcdefghijklmnopqrstuvwxyz";

template <class T0, class T1>
inline ostream &operator<<(ostream &out, pair<T0, T1> &a) {
  return out << "{" << a.first << ", " << a.second << "}";
}

template <class T0, class T1, class T2>
inline ostream &operator<<(ostream &out, tuple<T0, T1, T2> &a) {
  return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a)
             << "}";
}

template <class T0, class T1, class T2, class T3>
inline ostream &operator<<(ostream &out, tuple<T0, T1, T2, T3> &a) {
  return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a)
             << ", " << get<3>(a) << "}";
}

template <class T> inline ostream &operator<<(ostream &out, vector<T> &a) {
  out << "[";
  fori(i, a.size()) out << a[i]
                        << vector<string>{", ", "]  "}[i + 1 == a.size()];
  return out;
}

void smain();

signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);

#ifdef RUS_HOME
  freopen("input.txt", "r", stdin);
  clock_t start = clock();
#endif
  // freopen("input.txt", "r", stdin);
  // freopen("output.txt", "w", stdout);
  cout << setprecision(12) << fixed;
  smain();
#ifdef RUS_HOME
  cout << "\n\nTOTAL EXECUTION TIME: "
       << float(clock() - start) / CLOCKS_PER_SEC << endl;
#endif
}
const int oo = 1e9;
const int N = 1e5 + 100;
int MOD = 1e9 + 7;

vi gx[N], gy[N];
vi cur(N);
vi p[N];

void uni(int a, int b) {
  a = cur[a];
  b = cur[b];
  if (a == b)
    return;
  if (p[a].size() > p[b].size())
    swap(a, b);
  for (int i = 0; i < p[a].size(); i++) {
    p[b].push_back(p[a][i]);
    cur[p[a][i]] = b;
  }
  p[a].clear();
}

void smain() {

  int n;
  cin >> n;
  vi x(n), y(n);
  for (int i = 0; i < n; i++) {
    cin >> x[i] >> y[i];
    gx[x[i]].push_back(i);
    gy[y[i]].push_back(i);
    cur[i] = i;
    p[i].push_back(i);
  }

  for (int i = 0; i < N; i++) {
    for (int j = 1; j < gx[i].size(); j++) {
      uni(gx[i][j], gx[i][j - 1]);
    }
    for (int j = 1; j < gy[i].size(); j++) {
      uni(gy[i][j], gy[i][j - 1]);
    }
  }
  int ans = 0;
  for (int i = 0; i < N; i++) {
    set<int> sx, sy;
    for (int j = 0; j < p[i].size(); j++) {
      sx.insert(x[p[i][j]]);
      sy.insert(y[p[i][j]]);
    }
    ans += sx.size() * sy.size();
  }
  cout << ans - n;
}