Problem p02906 (C++)

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

using namespace std;

using int64 = long long;
const int mod = 998244353;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;

template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << p.first << " " << p.second;
  return os;
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

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

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &in : v)
    is >> in;
  return is;
}

template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  return a > b && (a = b, true);
}

template <typename T = int64> vector<T> make_v(size_t a) {
  return vector<T>(a);
}

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}

template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}

template <typename F> struct FixPoint : F {
  FixPoint(F &&f) : F(forward<F>(f)) {}

  template <typename... Args> decltype(auto) operator()(Args &&...args) const {
    return F::operator()(*this, forward<Args>(args)...);
  }
};

template <typename F> inline decltype(auto) MFP(F &&f) {
  return FixPoint<F>{forward<F>(f)};
}

struct UnionFind {
  vector<int> data;

  UnionFind(int sz) { data.assign(sz, -1); }

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

  int find(int k) {
    if (data[k] < 0)
      return (k);
    return (data[k] = find(data[k]));
  }

  int size(int k) { return (-data[find(k)]); }
};

int main() {
  int64 N, M, Q;
  cin >> N >> M >> Q;
  UnionFind uf(N);
  vector<int> A(N), B(N), C(N);
  for (int i = 0; i < Q; i++) {
    cin >> A[i] >> B[i] >> C[i];
  }

  int used = 0;
  for (int i = 0; i < Q; i++) {
    if (C[i] == 0)
      if (uf.unite(A[i], B[i]))
        ++used;
  }

  auto Yes = []() {
    cout << "Yes" << endl;
    exit(0);
  };
  auto No = []() {
    cout << "No" << endl;
    exit(0);
  };

  for (int i = 0; i < Q; i++) {
    if (C[i] == 1) {
      if (uf.find(A[i]) == uf.find(B[i]))
        No();
    }
  }

  vector<int> rot;
  for (int i = 0; i < N; i++) {
    if (uf.find(i) == i)
      rot.emplace_back(i);
  }

  if (rot.size() == 1) {
    if (used == M)
      Yes();
    else
      No();
  } else if (rot.size() == 2) {

    for (int i = 0; i < Q; i++) {
      if (C[i] == 1)
        No();
    }
    ++used;
    if (used == M)
      Yes();
    else
      No();
  } else {
    UnionFind uf2(N);
    int64 low = used, high = used;

    set<int> appear;
    for (int i = 0; i < Q; i++) {
      if (C[i] == 1) {
        appear.emplace(uf.find(A[i]));
        appear.emplace(uf.find(B[i]));
      }
    }
    int64 v = rot.size();
    high += v * (v - 1) / 2;
    low += appear.size();

    if (low <= M && M <= high)
      Yes();
    else
      No();
  }
}


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

using namespace std;

using int64 = long long;
const int mod = 998244353;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;

template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << p.first << " " << p.second;
  return os;
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

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

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &in : v)
    is >> in;
  return is;
}

template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  return a > b && (a = b, true);
}

template <typename T = int64> vector<T> make_v(size_t a) {
  return vector<T>(a);
}

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}

template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}

template <typename F> struct FixPoint : F {
  FixPoint(F &&f) : F(forward<F>(f)) {}

  template <typename... Args> decltype(auto) operator()(Args &&...args) const {
    return F::operator()(*this, forward<Args>(args)...);
  }
};

template <typename F> inline decltype(auto) MFP(F &&f) {
  return FixPoint<F>{forward<F>(f)};
}

struct UnionFind {
  vector<int> data;

  UnionFind(int sz) { data.assign(sz, -1); }

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

  int find(int k) {
    if (data[k] < 0)
      return (k);
    return (data[k] = find(data[k]));
  }

  int size(int k) { return (-data[find(k)]); }
};

int main() {
  int64 N, M, Q;
  cin >> N >> M >> Q;
  UnionFind uf(N);
  vector<int> A(Q), B(Q), C(Q);
  for (int i = 0; i < Q; i++) {
    cin >> A[i] >> B[i] >> C[i];
  }

  int used = 0;
  for (int i = 0; i < Q; i++) {
    if (C[i] == 0)
      if (uf.unite(A[i], B[i]))
        ++used;
  }

  auto Yes = []() {
    cout << "Yes" << endl;
    exit(0);
  };
  auto No = []() {
    cout << "No" << endl;
    exit(0);
  };

  for (int i = 0; i < Q; i++) {
    if (C[i] == 1) {
      if (uf.find(A[i]) == uf.find(B[i]))
        No();
    }
  }

  vector<int> rot;
  for (int i = 0; i < N; i++) {
    if (uf.find(i) == i)
      rot.emplace_back(i);
  }

  if (rot.size() == 1) {
    if (used == M)
      Yes();
    else
      No();
  } else if (rot.size() == 2) {

    for (int i = 0; i < Q; i++) {
      if (C[i] == 1)
        No();
    }
    ++used;
    if (used == M)
      Yes();
    else
      No();
  } else {
    UnionFind uf2(N);
    int64 low = used, high = used;

    set<int> appear;
    for (int i = 0; i < Q; i++) {
      if (C[i] == 1) {
        appear.emplace(uf.find(A[i]));
        appear.emplace(uf.find(B[i]));
      }
    }
    int64 v = rot.size();
    high += v * (v - 1) / 2;
    low += appear.size();

    if (low <= M && M <= high)
      Yes();
    else
      No();
  }
}