Problem p03682 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <utility>
#include <vector>

using namespace std;

/* template */

using ll = long long;

void debug_out() { std::cout << std::endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...)                                                             \
  cout << "debug: ";                                                           \
  debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

#define rep(i, a, n) for (int i = (int)(a); i < (int)(n); i++)
#define rrep(i, a, n) for (int i = ((int)(n - 1)); i >= (int)(a); i--)
#define Rep(i, a, n) for (long long i = (long long)(a); i < (long long)(n); i++)
#define RRep(i, a, n)                                                          \
  for (long long i = ((long long)(n - 1ll)); i >= (long long)(a); i--)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

struct Edge {
  int to;
  ll weight;
  Edge(int t, ll w) : to(t), weight(w) {}
};

struct edge {
  int from;
  int to;
  ll weight;
  edge(int f, int t, ll w) : from(f), to(t), weight(w) {}
};

using Graph = vector<vector<Edge>>;
using graph = vector<vector<int>>;
using edges = vector<edge>;

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> T lcm(T a, T b) { return (a * b) / gcd(a, b); }

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;
  }
}

constexpr ll LNF = 1LL << 50;

constexpr int INF = 1e9 + 7;

const long double PI = 3.14159265358979323846;

vector<int> dx = {1, 0, -1, 1, -1, 0};
vector<int> dy = {1, 1, 1, 0, 0, -1};

/* template */

struct UnionFind {
private:
  std::vector<int> par;

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

public:
  UnionFind(int n = 0) : par(n, -1) {}

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

  bool unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y)
      return false;
    if (par[x] > par[y])
      std::swap(x, y);
    par[x] += par[y];
    par[y] = x;
    return true;
  }

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

  int count_group() {
    int c = 0;
    for (int i = 0; i < par.size(); i++) {
      if (par[i] < 0)
        c++;
    }
    return c;
  }
};

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  using pll = pair<ll, ll>;

  int n;
  cin >> n;
  vector<pair<ll, ll>> x(n);
  vector<pair<ll, ll>> y(n);
  map<int, pair<ll, ll>> m;
  rep(i, 0, n) {
    cin >> x[i].first;
    x[i].second = i;
    cin >> y[i].first;
    y[i].second = i;
    m[i] = make_pair(x[i].first, y[i].first);
  }
  sort(all(x));
  sort(all(y));
  priority_queue<pair<ll, pll>, vector<pair<ll, pll>>, greater<pair<ll, pll>>>
      que;
  rep(i, 0, n - 1) {
    que.push(make_pair(x[i + 1].first - x[i].first,
                       pll(x[i + 1].second, x[i].second)));
    que.push(make_pair(y[i + 1].first - y[i].first,
                       pll(y[i + 1].second, y[i].second)));
  }
  UnionFind uf(n);
  ll ans = 0;
  while (uf.count_group() > 1) {
    auto nxt = que.top();
    pll nx = nxt.second;
    que.pop();
    if (uf.same(nx.first, nx.second)) {
      continue;
    } else {
      uf.unite(nx.first, nx.second);
      ans += nxt.first;
    }
  }
  cout << ans << endl;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <utility>
#include <vector>

using namespace std;

/* template */

using ll = long long;

void debug_out() { std::cout << std::endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...)                                                             \
  cout << "debug: ";                                                           \
  debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

#define rep(i, a, n) for (int i = (int)(a); i < (int)(n); i++)
#define rrep(i, a, n) for (int i = ((int)(n - 1)); i >= (int)(a); i--)
#define Rep(i, a, n) for (long long i = (long long)(a); i < (long long)(n); i++)
#define RRep(i, a, n)                                                          \
  for (long long i = ((long long)(n - 1ll)); i >= (long long)(a); i--)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

struct Edge {
  int to;
  ll weight;
  Edge(int t, ll w) : to(t), weight(w) {}
};

struct edge {
  int from;
  int to;
  ll weight;
  edge(int f, int t, ll w) : from(f), to(t), weight(w) {}
};

using Graph = vector<vector<Edge>>;
using graph = vector<vector<int>>;
using edges = vector<edge>;

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> T lcm(T a, T b) { return (a * b) / gcd(a, b); }

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;
  }
}

constexpr ll LNF = 1LL << 50;

constexpr int INF = 1e9 + 7;

const long double PI = 3.14159265358979323846;

vector<int> dx = {1, 0, -1, 1, -1, 0};
vector<int> dy = {1, 1, 1, 0, 0, -1};

/* template */

struct UnionFind {
private:
  std::vector<int> par;

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

public:
  UnionFind(int n = 0) : par(n, -1) {}

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

  bool unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y)
      return false;
    if (par[x] > par[y])
      std::swap(x, y);
    par[x] += par[y];
    par[y] = x;
    return true;
  }

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

  int count_group() {
    int c = 0;
    for (int i = 0; i < par.size(); i++) {
      if (par[i] < 0)
        c++;
    }
    return c;
  }
};

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  using pll = pair<ll, ll>;

  int n;
  cin >> n;
  vector<pair<ll, ll>> x(n);
  vector<pair<ll, ll>> y(n);
  map<int, pair<ll, ll>> m;
  rep(i, 0, n) {
    cin >> x[i].first;
    x[i].second = i;
    cin >> y[i].first;
    y[i].second = i;
    m[i] = make_pair(x[i].first, y[i].first);
  }
  sort(all(x));
  sort(all(y));
  priority_queue<pair<ll, pll>, vector<pair<ll, pll>>, greater<pair<ll, pll>>>
      que;
  rep(i, 0, n - 1) {
    que.push(make_pair(x[i + 1].first - x[i].first,
                       pll(x[i + 1].second, x[i].second)));
    que.push(make_pair(y[i + 1].first - y[i].first,
                       pll(y[i + 1].second, y[i].second)));
  }
  UnionFind uf(n);
  ll ans = 0;
  while (!que.empty()) {
    auto nxt = que.top();
    pll nx = nxt.second;
    que.pop();
    if (uf.same(nx.first, nx.second)) {
      continue;
    } else {
      uf.unite(nx.first, nx.second);
      ans += nxt.first;
    }
  }
  cout << ans << endl;
}