Problem p02573 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define pii pair<int, int>
#define pp pair<pair<ll, ll>, pair<ll, ll>>
#define pll pair<ll, ll>
#define ppll pair<ll, pll>
#define pdd pair<double, double>
#define vii vector<int>
#define vll vector<ll>
#define mat vector<vector<ll>>
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define eb emplace_back
#define fi first
#define sc second
#define rep(i, n) for (ll i = 0; i < n; i++)
#define rep2(i, a, b) for (ll i = a; i < b; i++)
#define repr(i, n) for (ll i = n - 1; i >= 0; i--)
#define all(x) x.begin(), x.end()
#define sz(x) (ll)(x).size()
#define pq priority_queue<ll>
#define pqg priority_queue<ll, vector<ll>, greater<ll>>
#define LB(v, x) (lower_bound(v.begin(), v.end(), x) - v.begin())
#define UB(v, x) (upper_bound(v.begin(), v.end(), x) - v.begin())
#define ERASE(v)                                                               \\
  sort(v.begin(), v.end());                                                    \\
  v.erase(unique(v.begin(), v.end()), v.end())
#define int ll
// #define ll int
using namespace std;
const ll INF = 1 << 29;
const ll LLINF = (1LL << 60LL);
const ll MOD = 1000000007;
const int MAX_V = 500;
// const ll mod = 998244353;
const ll MAX = 2100000;
const double pi = acos(-1);
const double eps = 1e-10;
ll dx[8] = {1, 0, -1, 0, 1, -1, 1, -1};
ll dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

struct UnionFind {
  vector<ll> par;

  UnionFind(ll n) : par(n, -1) {}
  void init(ll n) { par.assign(n, -1); }

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

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

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

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

  void print(ll x) {
    rep(i, x) { cout << par[i] << endl; }
    return;
  }
};

void solve() {
  ll n, m;
  cin >> n >> m;
  ll a[200010], b[200010];
  rep(i, m) {
    cin >> a[i] >> b[i];
    a[i]--, b[i]--;
  }
  UnionFind uf(n);
  rep(i, m) { uf.unite(a[i], b[i]); }
  ll ans = 0;
  rep(i, n) {
    // cout<<i<<" "<<uf.size(i)<<endl;

    chmax(ans, uf.size(i));
  }
  cout << ans << endl;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);

  ll t = 1;
  rep(i, t) { solve(); }

  return 0;
}

Error: -11

Fixed submission:

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define pii pair<int, int>
#define pp pair<pair<ll, ll>, pair<ll, ll>>
#define pll pair<ll, ll>
#define ppll pair<ll, pll>
#define pdd pair<double, double>
#define vii vector<int>
#define vll vector<ll>
#define mat vector<vector<ll>>
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define eb emplace_back
#define fi first
#define sc second
#define rep(i, n) for (ll i = 0; i < n; i++)
#define rep2(i, a, b) for (ll i = a; i < b; i++)
#define repr(i, n) for (ll i = n - 1; i >= 0; i--)
#define all(x) x.begin(), x.end()
#define sz(x) (ll)(x).size()
#define pq priority_queue<ll>
#define pqg priority_queue<ll, vector<ll>, greater<ll>>
#define LB(v, x) (lower_bound(v.begin(), v.end(), x) - v.begin())
#define UB(v, x) (upper_bound(v.begin(), v.end(), x) - v.begin())
#define ERASE(v)                                                               \\
  sort(v.begin(), v.end());                                                    \\
  v.erase(unique(v.begin(), v.end()), v.end())
#define int ll
// #define ll int
using namespace std;
const ll INF = 1 << 29;
const ll LLINF = (1LL << 60LL);
const ll MOD = 1000000007;
const int MAX_V = 500;
// const ll mod = 998244353;
const ll MAX = 2100000;
const double pi = acos(-1);
const double eps = 1e-10;
ll dx[8] = {1, 0, -1, 0, 1, -1, 1, -1};
ll dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

struct UnionFind {
  vector<ll> par;

  UnionFind(ll n) : par(n, -1) {}
  void init(ll n) { par.assign(n, -1); }

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

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

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

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

  void print(ll x) {
    rep(i, x) { cout << par[i] << endl; }
    return;
  }
};

void solve() {
  ll n, m;
  cin >> n >> m;
  ll a[200010], b[200010];
  rep(i, m) cin >> a[i] >> b[i];
  UnionFind uf(n);
  rep(i, m) { uf.unite(a[i], b[i]); }
  ll ans = 0;
  rep2(i, 1, n + 1) {
    // cout<<i<<" "<<uf.size(i)<<endl;

    chmax(ans, uf.size(i));
  }
  cout << ans << endl;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);

  ll t = 1;
  rep(i, t) { solve(); }

  return 0;
}