Problem p02998 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back
#define ub upper_bound
#define lb upper_bound
#define mp make_pair
#define F first
#define S second
#define FOR(i, a, b) for (int(i) = (a); (i) < (b); (i)++)
#define REP(i, n) FOR(i, 0, n)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define SORT(c) sort((c).begin(), (c).end())
#define ve vector
#define vi vector<int>
#define vp vector<pair<int, int>>
#define vvi vector<vector<int>>

typedef long long ll;
const ll INF = LLONG_MAX - 100;
const ll mod = 1e9 + 7;
const int MAX_N = 2e5 + 5;
int dx[] = {-1, 0, 1, 0}, dy[] = {0, 1, 0, -1};
vector<ll> prime;

int fac[MAX_N], inv[MAX_N];

template <class T = ll> T in() {
  T x;
  cin >> x;
  return (x);
}
void DEBUG(vector<int> a) {
  for (int i = 0; i < a.size(); i++)
    cout << a[i] << " ";
  cout << endl;
}
ll GCD(ll a, ll b) {
  ll c;
  while (b != 0) {
    c = a % b;
    a = b;
    b = c;
  }
  return a;
}
ll LCM(ll a, ll b) { return a * b / GCD(a, b); }
ll POW(ll a, ll b, bool usemod = true) {
  ll c = 1LL;
  while (b > 0) {
    if (b & 1LL) {
      if (!usemod)
        c *= a;
      else
        c = a * c % mod;
    }
    if (!usemod)
      a *= a;
    else
      a = a * a % mod;
    b >>= 1LL;
  }
  return c;
}
void _nCr() {
  fac[0] = 1LL;
  for (int i = 1LL; i < MAX_N; i++) {
    fac[i] = fac[i - 1LL] * i % mod;
  }
  for (int i = 0; i < MAX_N; i++) {
    inv[i] = POW(fac[i], mod - 2);
  }
}
ll nCr(ll n, ll r) { return (fac[n] * inv[r] % mod) * inv[n - r] % mod; }
void PRI(ll n) {
  bool a[n + 1LL];
  for (int i = 0; i < n + 1LL; i++) {
    a[i] = 1LL;
  }
  for (int i = 2; i < n + 1LL; i++) {
    if (a[i]) {
      prime.pb(i);
      ll b = i;
      while (b <= n) {
        a[b] = 0;
        b += i;
      }
    }
  }
}
template <typename T> T chmin(T &a, T b) {
  if (a > b)
    a = b;
  return a;
}
template <typename T> T chmax(T &a, T b) {
  if (a < b)
    a = b;
  return b;
}

class UnionFind {
private:
  vector<ll> par;

public:
  UnionFind(int N) { par = vector<int>(N, -1); }
  int find(int x);
  ll size(int x);
  void unite(int x, int y);
  bool same(int x, int y);
};

int UnionFind::find(int x) {
  if (par[x] < 0)
    return x;
  else
    return par[x] = find(par[x]);
}

ll UnionFind::size(int x) { return -par[find(x)]; }

void UnionFind::unite(int x, int y) {
  x = find(x);
  y = find(y);
  if (x == y)
    return;
  // 大きい方に小さい方をくっ付ける
  if (size(x) < size(y))
    swap(x, y);
  par[x] += par[y];
  par[y] = x;
}

bool UnionFind::same(int x, int y) {
  x = find(x);
  y = find(y);
  return x == y;
}

int MAX = 11000;

bool solve() {
  int n;
  cin >> n;
  UnionFind uf(MAX * 2);
  REP(i, n) {
    int x, y;
    cin >> x >> y;
    uf.unite(x, y + MAX);
  }
  map<int, int> mx, my;
  REP(i, MAX) mx[uf.find(i)]++;
  FOR(i, MAX, 2 * MAX) my[uf.find(i)]++;
  int ans = 0;
  REP(i, 2 * MAX) ans += mx[i] * my[i];
  ans -= n;
  cout << ans << endl;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back
#define ub upper_bound
#define lb upper_bound
#define mp make_pair
#define F first
#define S second
#define FOR(i, a, b) for (int(i) = (a); (i) < (b); (i)++)
#define REP(i, n) FOR(i, 0, n)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define SORT(c) sort((c).begin(), (c).end())
#define ve vector
#define vi vector<int>
#define vp vector<pair<int, int>>
#define vvi vector<vector<int>>

typedef long long ll;
const ll INF = LLONG_MAX - 100;
const ll mod = 1e9 + 7;
const int MAX_N = 2e5 + 5;
int dx[] = {-1, 0, 1, 0}, dy[] = {0, 1, 0, -1};
vector<ll> prime;

int fac[MAX_N], inv[MAX_N];

template <class T = ll> T in() {
  T x;
  cin >> x;
  return (x);
}
void DEBUG(vector<int> a) {
  for (int i = 0; i < a.size(); i++)
    cout << a[i] << " ";
  cout << endl;
}
ll GCD(ll a, ll b) {
  ll c;
  while (b != 0) {
    c = a % b;
    a = b;
    b = c;
  }
  return a;
}
ll LCM(ll a, ll b) { return a * b / GCD(a, b); }
ll POW(ll a, ll b, bool usemod = true) {
  ll c = 1LL;
  while (b > 0) {
    if (b & 1LL) {
      if (!usemod)
        c *= a;
      else
        c = a * c % mod;
    }
    if (!usemod)
      a *= a;
    else
      a = a * a % mod;
    b >>= 1LL;
  }
  return c;
}
void _nCr() {
  fac[0] = 1LL;
  for (int i = 1LL; i < MAX_N; i++) {
    fac[i] = fac[i - 1LL] * i % mod;
  }
  for (int i = 0; i < MAX_N; i++) {
    inv[i] = POW(fac[i], mod - 2);
  }
}
ll nCr(ll n, ll r) { return (fac[n] * inv[r] % mod) * inv[n - r] % mod; }
void PRI(ll n) {
  bool a[n + 1LL];
  for (int i = 0; i < n + 1LL; i++) {
    a[i] = 1LL;
  }
  for (int i = 2; i < n + 1LL; i++) {
    if (a[i]) {
      prime.pb(i);
      ll b = i;
      while (b <= n) {
        a[b] = 0;
        b += i;
      }
    }
  }
}
template <typename T> T chmin(T &a, T b) {
  if (a > b)
    a = b;
  return a;
}
template <typename T> T chmax(T &a, T b) {
  if (a < b)
    a = b;
  return b;
}

class UnionFind {
private:
  vector<ll> par;

public:
  UnionFind(int N) { par = vector<int>(N, -1); }
  int find(int x);
  ll size(int x);
  void unite(int x, int y);
  bool same(int x, int y);
};

int UnionFind::find(int x) {
  if (par[x] < 0)
    return x;
  else
    return par[x] = find(par[x]);
}

ll UnionFind::size(int x) { return -par[find(x)]; }

void UnionFind::unite(int x, int y) {
  x = find(x);
  y = find(y);
  if (x == y)
    return;
  // 大きい方に小さい方をくっ付ける
  if (size(x) < size(y))
    swap(x, y);
  par[x] += par[y];
  par[y] = x;
}

bool UnionFind::same(int x, int y) {
  x = find(x);
  y = find(y);
  return x == y;
}

int MAX = 110000;

bool solve() {
  int n;
  cin >> n;
  UnionFind uf(MAX * 2);
  REP(i, n) {
    int x, y;
    cin >> x >> y;
    uf.unite(x, y + MAX);
  }
  map<int, int> mx, my;
  REP(i, MAX) mx[uf.find(i)]++;
  FOR(i, MAX, 2 * MAX) my[uf.find(i)]++;
  int ans = 0;
  REP(i, 2 * MAX) ans += mx[i] * my[i];
  ans -= n;
  cout << ans << endl;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
}