Problem p02540 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <complex>
#include <cstring>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

using namespace std;
// using namespace atcoder;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define RREP(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define FOR(i, a, n) for (int i = (a); i < (n); ++i)
#define RFOR(i, a, n) for (int i = (int)(n)-1; i >= (a); --i)

#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()

#define DUMP(x) cerr << #x << " = " << (x) << endl
#define DEBUG(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl;

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[";
  REP(i, SZ(v)) {
    if (i)
      os << ", ";
    os << v[i];
  }
  return os << "]";
}

template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  return os << "(" << p.first << " " << p.second << ")";
}

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

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

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;

const ll MOD = 1e9 + 7;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;
const ld eps = 1e-9;

// edit

struct UnionFind {
  vector<int> par, sz;

  UnionFind(int n) : par(n), sz(n, 1) {
    for (int i = 0; i < n; ++i)
      par[i] = i;
  }

  int root(int x) {
    if (par[x] == x)
      return x;
    return par[x] = root(par[x]);
  }

  void merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return;
    if (sz[x] < sz[y])
      swap(x, y);
    par[y] = x;
    sz[x] += sz[y];
    sz[y] = 0;
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  int size(int x) { return sz[root(x)]; }
};

void solve() {
  int N;
  cin >> N;
  vector<pair<int, int>> xy(N);
  vector<pair<int, int>> xi(N);
  REP(i, N) {
    cin >> xy[i].first >> xy[i].second;
    xy[i].first--;
    xy[i].second--;
    xi[i] = {xy[i].first, i};
  }
  sort(ALL(xy));

  vector<int> gmin(N), gmax(N);
  for (int i = 0; i < N; ++i) {
    gmin[i] = xy[i].second;
    gmax[i] = xy[i].second;
  }

  UnionFind uf(N);
  while (true) {
    bool merge = false;
    for (int i = 0; i + 1 < N; ++i) {
      if (uf.issame(i, i + 1)) {
        continue;
      }
      if (gmin[uf.root(i)] < gmax[uf.root(i + 1)]) {
        gmin[uf.root(i)] = min(gmin[uf.root(i)], gmin[uf.root(i + 1)]);
        gmax[uf.root(i)] = max(gmax[uf.root(i)], gmax[uf.root(i + 1)]);

        gmin[uf.root(i + 1)] = gmin[uf.root(i)];
        gmax[uf.root(i + 1)] = gmax[uf.root(i)];

        //                cerr << "merge " << uf.root(i) << " " << uf.root(i +
        //                1) << endl;

        uf.merge(i, i + 1);
        merge = true;
      }
    }

    if (!merge)
      break;
  }
  for (int i = 0; i < N; ++i) {
    cout << uf.size(xi[i].first) << endl;
  }
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  //    std::ifstream in("input.txt");
  //    std::cin.rdbuf(in.rdbuf());

  solve();

  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <complex>
#include <cstring>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

using namespace std;
// using namespace atcoder;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define RREP(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define FOR(i, a, n) for (int i = (a); i < (n); ++i)
#define RFOR(i, a, n) for (int i = (int)(n)-1; i >= (a); --i)

#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()

#define DUMP(x) cerr << #x << " = " << (x) << endl
#define DEBUG(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl;

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[";
  REP(i, SZ(v)) {
    if (i)
      os << ", ";
    os << v[i];
  }
  return os << "]";
}

template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  return os << "(" << p.first << " " << p.second << ")";
}

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

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

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;

const ll MOD = 1e9 + 7;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;
const ld eps = 1e-9;

// edit

struct UnionFind {
  vector<int> par, sz;

  UnionFind(int n) : par(n), sz(n, 1) {
    for (int i = 0; i < n; ++i)
      par[i] = i;
  }

  int root(int x) {
    if (par[x] == x)
      return x;
    return par[x] = root(par[x]);
  }

  void merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return;
    if (sz[x] < sz[y])
      swap(x, y);
    par[y] = x;
    sz[x] += sz[y];
    sz[y] = 0;
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  int size(int x) { return sz[root(x)]; }
};

void solve() {
  int N;
  cin >> N;
  vector<pair<int, int>> xy(N);
  vector<pair<int, int>> xi(N);
  REP(i, N) {
    cin >> xy[i].first >> xy[i].second;
    xy[i].first--;
    xy[i].second--;
    xi[i] = {xy[i].first, i};
  }
  sort(ALL(xy));

  vector<int> gmin(N), gmax(N);
  for (int i = 0; i < N; ++i) {
    gmin[i] = xy[i].second;
    gmax[i] = xy[i].second;
  }

  UnionFind uf(N);
  while (true) {
    bool merge = false;
    for (int i = 0; i + 1 < N; ++i) {
      if (uf.issame(i, i + 1)) {
        continue;
      }
      if (gmin[uf.root(i)] < gmax[uf.root(i + 1)]) {
        gmin[uf.root(i)] = min(gmin[uf.root(i)], gmin[uf.root(i + 1)]);
        gmax[uf.root(i)] = max(gmax[uf.root(i)], gmax[uf.root(i + 1)]);

        gmin[uf.root(i + 1)] = gmin[uf.root(i)];
        gmax[uf.root(i + 1)] = gmax[uf.root(i)];

        //                cerr << "merge " << uf.root(i) << " " << uf.root(i +
        //                1) << endl;

        uf.merge(i, i + 1);
        merge = true;
      }
    }

    for (int i = N - 2; i >= 0; --i) {
      if (uf.issame(i, i + 1)) {
        continue;
      }
      if (gmin[uf.root(i)] < gmax[uf.root(i + 1)]) {
        gmin[uf.root(i)] = min(gmin[uf.root(i)], gmin[uf.root(i + 1)]);
        gmax[uf.root(i)] = max(gmax[uf.root(i)], gmax[uf.root(i + 1)]);

        gmin[uf.root(i + 1)] = gmin[uf.root(i)];
        gmax[uf.root(i + 1)] = gmax[uf.root(i)];

        //                cerr << "merge " << uf.root(i) << " " << uf.root(i +
        //                1) << endl;

        uf.merge(i, i + 1);
        merge = true;
      }
    }
    if (!merge)
      break;
  }
  for (int i = 0; i < N; ++i) {
    cout << uf.size(xi[i].first) << endl;
  }
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  //    std::ifstream in("input.txt");
  //    std::cin.rdbuf(in.rdbuf());

  solve();

  return 0;
}