Problem p02573 (C++)

Buggy submission (status: Runtime Error):

/*
LANG:C++
PROB:

*/
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <functional>
#include <iostream>
// #define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define forn(i, n) for (int i = 0; i < (int)(n); ++i)
#define for1(i, n) for (int i = 1; i <= (int)(n); ++i)
#define ford(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define fore(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)

using namespace __gnu_pbds;
using namespace std;

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<vi> vvi;
typedef long long i64;
typedef vector<i64> vi64;
typedef vector<vi64> vvi64;
typedef pair<i64, i64> pi64;
typedef double ld;
typedef unsigned long long ui64;

template <class T> bool uin(T &a, T b) { return a > b ? (a = b, true) : false; }
template <class T> bool uax(T &a, T b) { return a < b ? (a = b, true) : false; }
const int mod = 1000000007;
i64 poww(i64 a, i64 b) {
  a %= mod;
  i64 res = 1;
  while (b) {
    if (b & 1)
      res = res * a % mod;

    a = a * a % mod;
    b /= 2;
  }
  return res;
}
i64 inv(i64 a) { return poww(a, mod - 2); }
int par[200009], sz[100009];
int p(int x) {
  if (x == par[x])
    return x;

  return par[x] = p(par[x]);
}
void unite(int x, int y) {
  x = p(x);
  y = p(y);
  if (x == y)
    return;
  if (sz[x] > sz[y])
    swap(x, y);
  sz[y] += sz[x];
  par[x] = y;
}
void solve() {
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= n; i++)
    par[i] = i, sz[i] = 1;
  forn(i, m) {
    int x, y;
    cin >> x >> y;
    unite(x, y);
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    ans = max(ans, sz[p(i)]);
  }
  cout << ans;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  int t = 1;
  while (t--) {
    solve();
  }

  return 0;
}


Fixed submission:

/*
LANG:C++
PROB:

*/
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <functional>
#include <iostream>
// #define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define forn(i, n) for (int i = 0; i < (int)(n); ++i)
#define for1(i, n) for (int i = 1; i <= (int)(n); ++i)
#define ford(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define fore(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)

using namespace __gnu_pbds;
using namespace std;

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<vi> vvi;
typedef long long i64;
typedef vector<i64> vi64;
typedef vector<vi64> vvi64;
typedef pair<i64, i64> pi64;
typedef double ld;
typedef unsigned long long ui64;

template <class T> bool uin(T &a, T b) { return a > b ? (a = b, true) : false; }
template <class T> bool uax(T &a, T b) { return a < b ? (a = b, true) : false; }
const int mod = 1000000007;
i64 poww(i64 a, i64 b) {
  a %= mod;
  i64 res = 1;
  while (b) {
    if (b & 1)
      res = res * a % mod;

    a = a * a % mod;
    b /= 2;
  }
  return res;
}
i64 inv(i64 a) { return poww(a, mod - 2); }
int par[200009], sz[200009];
int p(int x) {
  if (x == par[x])
    return x;

  return par[x] = p(par[x]);
}
void unite(int x, int y) {
  x = p(x);
  y = p(y);
  if (x == y)
    return;
  if (sz[x] > sz[y])
    swap(x, y);
  sz[y] += sz[x];
  par[x] = y;
}
void solve() {
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= n; i++)
    par[i] = i, sz[i] = 1;
  forn(i, m) {
    int x, y;
    cin >> x >> y;
    unite(x, y);
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    ans = max(ans, sz[p(i)]);
  }
  cout << ans;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  int t = 1;
  while (t--) {
    solve();
  }

  return 0;
}