Problem p02536 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <array>
#include <assert.h>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstdio>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
int INF = 1e9 + 7;
int mod = 998244353;
long double PI =
    3.141592653589793238462643383279502884197169399375105820974944592307816406286208998626034825342117;
struct Edge {
  long long to;
  long long cost;
};
void dijkstra(
    const vector<vector<Edge>> &G, long long s,
    vector<long long> &dis) { // Gは隣接グラフ,sは始点,距離の結果をdisに格納
  long long N = G.size();
  dis.resize(N, INF);
  priority_queue<pair<int, int>, vector<pair<int, int>>,
                 greater<pair<int, int>>>
      pq; // 「仮の最短距離, 頂点」が小さい順に並ぶ
  dis[s] = 0;
  pq.emplace(dis[s], s);
  while (!pq.empty()) {
    pair<int, int> p = pq.top();
    pq.pop();
    int v = p.second;
    if (dis[v] < p.first) {
      continue;
    }
    for (auto &e : G[v]) {
      if (dis[e.to] > dis[v] + e.cost) {
        dis[e.to] = dis[v] + e.cost;
        pq.emplace(dis[e.to], e.to);
      }
    }
  }
  return;
}
long double kodohou(long double N) { return N * 180.0 / PI; }
struct mint {
  int x;
  mint(int x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(int t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
struct UnionFind {
  vector<int> par, size;
  UnionFind(int x) {
    par.resize(x);
    size.resize(x, 1);
    for (int i = 0; i < x; i++) {
      par[i] = i;
    }
  }
  int find(int x) {
    if (par[x] == x)
      return x;
    return par[x] = find(par[x]);
  }
  bool same(int x, int y) { return find(x) == find(y); }
  int consize(int x) { return size[find(x)]; }
  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y)
      return;
    if (size[x] < size[y]) {
      par[x] = y;
      size[y] += size[x];
    } else {
      par[y] = x;
      size[x] += size[y];
    }
  }
};
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;
}
long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
bool IsPrime(int num) {
  if (num < 2)
    return false;
  else if (num == 2)
    return true;
  else if (num % 2 == 0)
    return false;
  double sqrtNum = sqrt(num);
  for (int i = 3; i <= sqrtNum; i += 2) {
    if (num % i == 0) {
      return false;
    }
  }
  return true;
}
signed gcd(long long x, long long y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}
signed lcm(long long x, long long y) { return x / gcd(x, y) * y; }
long long RepeatSquaring(long long N, long long P, long long M) {
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    long long t = RepeatSquaring(N, P / 2, M);
    return t * t % M;
  }
  return N * RepeatSquaring(N, P - 1, M);
}
int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
long long Fibonacci(long long A) {
  if (A == 1)
    return 1;
  vector<long long> B(A + 1);
  B[0] = 1;
  B[1] = 1;
  for (int i = 2; i <= A; i++) {
    B[i] = B[i - 1] + B[i - 2];
    B[i] %= mod;
  }
  return B[A];
}
int mod_pow(int x, int y) {
  int res = 1;
  while (y > 0) {
    if (y % 2) {
      res = res * x % mod;
    }
    x = x * x % mod;
    y /= 2;
  }
  return res;
}
int fac[100005], finv[100005], inv[100005];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < 100005; i++) {
    fac[i] = fac[i - 1] * i % mod;
    inv[i] = mod - inv[mod % i] * (mod / i) % mod;
    finv[i] = finv[i - 1] * inv[i] % mod;
  }
}
int COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % mod) % mod;
}
vector<int> sieve(int max) {
  vector<bool> prime(max + 1, true);
  vector<int> A;
  for (int i = 2; i <= max; ++i)
    if (prime[i]) {
      A.push_back(i);
      for (int j = 2; i * j <= max; ++j)
        prime[i * j] = false;
    }
  return A;
}
class smart_sieve {
  intmax_t L, R, M;
  vector<int> small;
  vector<vector<intmax_t>> large;
  vector<intmax_t> aux;

public:
  smart_sieve(intmax_t L, intmax_t R) : L(L), R(R), M(sqrt(R) + 1) {
    small.resize(M);
    iota(small.begin(), small.end(), 0);
    large.resize(R - L);
    aux.assign(R - L, 1);

    for (intmax_t i = 2; i * i < R; ++i) {
      if (small[i] < i)
        continue;
      small[i] = i;
      for (intmax_t j = i * i; j < M; j += i)
        if (small[j] == j)
          small[j] = i;

      for (intmax_t j = (L + i - 1) / i * i; j < R; j += i) {
        intmax_t k = j;
        do {
          if (aux[j - L] * aux[j - L] > R)
            break;

          large[j - L].push_back(i);
          aux[j - L] *= i;
          k /= i;
        } while (k % i == 0);
      }
    }
  }
};
int main() {
  int N, M;
  cin >> N >> M;
  vector<int> A(M);
  vector<int> B(M);
  UnionFind C(N);
  for (int i = 0; i < M; i++) {
    cin >> A[i] >> B[i];
    C.unite(A[i] - 1, B[i] - 1);
  }
  map<int, int> D;
  for (int i = 0; i < N; i++) {
    D[C.find(i)]++;
  }
  int ans = 0;
  for (int i = 0; i < N + 2; i++) {
    if (D[i] != 0)
      ans++;
  }
  cout << ans - 1 << endl;
}

Error: 0

Fixed submission:

#include <algorithm>
#include <array>
#include <assert.h>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstdio>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
int INF = 1e9 + 7;
int mod = 998244353;
long double PI =
    3.141592653589793238462643383279502884197169399375105820974944592307816406286208998626034825342117;
struct Edge {
  long long to;
  long long cost;
};
void dijkstra(
    const vector<vector<Edge>> &G, long long s,
    vector<long long> &dis) { // Gは隣接グラフ,sは始点,距離の結果をdisに格納
  long long N = G.size();
  dis.resize(N, INF);
  priority_queue<pair<int, int>, vector<pair<int, int>>,
                 greater<pair<int, int>>>
      pq; // 「仮の最短距離, 頂点」が小さい順に並ぶ
  dis[s] = 0;
  pq.emplace(dis[s], s);
  while (!pq.empty()) {
    pair<int, int> p = pq.top();
    pq.pop();
    int v = p.second;
    if (dis[v] < p.first) {
      continue;
    }
    for (auto &e : G[v]) {
      if (dis[e.to] > dis[v] + e.cost) {
        dis[e.to] = dis[v] + e.cost;
        pq.emplace(dis[e.to], e.to);
      }
    }
  }
  return;
}
long double kodohou(long double N) { return N * 180.0 / PI; }
struct mint {
  int x;
  mint(int x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(int t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
struct UnionFind {
  vector<int> par, size;
  UnionFind(int x) {
    par.resize(x);
    size.resize(x, 1);
    for (int i = 0; i < x; i++) {
      par[i] = i;
    }
  }
  int find(int x) {
    if (par[x] == x)
      return x;
    return par[x] = find(par[x]);
  }
  bool same(int x, int y) { return find(x) == find(y); }
  int consize(int x) { return size[find(x)]; }
  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y)
      return;
    if (size[x] < size[y]) {
      par[x] = y;
      size[y] += size[x];
    } else {
      par[y] = x;
      size[x] += size[y];
    }
  }
};
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;
}
long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
bool IsPrime(int num) {
  if (num < 2)
    return false;
  else if (num == 2)
    return true;
  else if (num % 2 == 0)
    return false;
  double sqrtNum = sqrt(num);
  for (int i = 3; i <= sqrtNum; i += 2) {
    if (num % i == 0) {
      return false;
    }
  }
  return true;
}
signed gcd(long long x, long long y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}
signed lcm(long long x, long long y) { return x / gcd(x, y) * y; }
long long RepeatSquaring(long long N, long long P, long long M) {
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    long long t = RepeatSquaring(N, P / 2, M);
    return t * t % M;
  }
  return N * RepeatSquaring(N, P - 1, M);
}
int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
long long Fibonacci(long long A) {
  if (A == 1)
    return 1;
  vector<long long> B(A + 1);
  B[0] = 1;
  B[1] = 1;
  for (int i = 2; i <= A; i++) {
    B[i] = B[i - 1] + B[i - 2];
    B[i] %= mod;
  }
  return B[A];
}
int mod_pow(int x, int y) {
  int res = 1;
  while (y > 0) {
    if (y % 2) {
      res = res * x % mod;
    }
    x = x * x % mod;
    y /= 2;
  }
  return res;
}
int fac[100005], finv[100005], inv[100005];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < 100005; i++) {
    fac[i] = fac[i - 1] * i % mod;
    inv[i] = mod - inv[mod % i] * (mod / i) % mod;
    finv[i] = finv[i - 1] * inv[i] % mod;
  }
}
int COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % mod) % mod;
}
vector<int> sieve(int max) {
  vector<bool> prime(max + 1, true);
  vector<int> A;
  for (int i = 2; i <= max; ++i)
    if (prime[i]) {
      A.push_back(i);
      for (int j = 2; i * j <= max; ++j)
        prime[i * j] = false;
    }
  return A;
}
class smart_sieve {
  intmax_t L, R, M;
  vector<int> small;
  vector<vector<intmax_t>> large;
  vector<intmax_t> aux;

public:
  smart_sieve(intmax_t L, intmax_t R) : L(L), R(R), M(sqrt(R) + 1) {
    small.resize(M);
    iota(small.begin(), small.end(), 0);
    large.resize(R - L);
    aux.assign(R - L, 1);

    for (intmax_t i = 2; i * i < R; ++i) {
      if (small[i] < i)
        continue;
      small[i] = i;
      for (intmax_t j = i * i; j < M; j += i)
        if (small[j] == j)
          small[j] = i;

      for (intmax_t j = (L + i - 1) / i * i; j < R; j += i) {
        intmax_t k = j;
        do {
          if (aux[j - L] * aux[j - L] > R)
            break;

          large[j - L].push_back(i);
          aux[j - L] *= i;
          k /= i;
        } while (k % i == 0);
      }
    }
  }
};
int main() {
  int N, M;
  cin >> N >> M;
  vector<int> A(M);
  vector<int> B(M);
  UnionFind C(N);
  for (int i = 0; i < M; i++) {
    cin >> A[i] >> B[i];
    C.unite(A[i], B[i]);
  }
  map<int, int> D;
  for (int i = 0; i < N; i++) {
    D[C.par[i]]++;
  }
  int ans = 0;
  for (int i = 0; i < N + 2; i++) {
    if (D[i] != 0)
      ans++;
  }
  cout << ans - 1 << endl;
}