Problem p02573 (C++)

Buggy submission (status: Runtime Error):
// It doesn't matter as long as you rise to the top - Katsuki Bakugo
#include <bits/stdc++.h>
using namespace std;

#define Fast_as_duck                                                           \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.tie(0)
#define pb push_back
#define forn(i, st, n) for (int i = st; i < n; i++)
#define rev(i, st, n) for (int i = st; i >= n; i--)
#define ss second
#define ff first
#define ll long long

typedef pair<int, int> pii;

const int N = 1e5 + 10, mod = 1000000007;

int visited[N];

void dfs(std::vector<int> path[], int u, int val, int visited[]) {
  visited[u] = val;
  // cout << u << " " << visited[u] << "\n";
  forn(i, 0, (int)path[u].size()) {
    if (visited[path[u][i]] == 0) {
      dfs(path, path[u][i], val, visited);
    }
  }
}

void solve() {

  int n, m;
  cin >> n >> m;

  std::vector<int> frnd[n + 1];
  int x, y;
  forn(i, 0, m) {
    cin >> x >> y;
    frnd[x].pb(y);
    frnd[y].pb(x);
  }

  // cout << "ans from here\n\n\n";

  // std::vector<int> visited(n+1 , 0);
  int val = 0;

  forn(i, 0, n) {
    if (visited[i + 1] == 0) {

      val++;
      visited[i + 1] = val;
      // cout << "dfs " << val << "\n";
      dfs(frnd, i + 1, val, visited);
    }
  }

  std::vector<int> ans(val + 1, 0);

  forn(i, 1, n + 1) {
    // cout << visited[i] << " ";
    ans[visited[i]]++;
  }

  sort(ans.begin(), ans.end());

  cout << ans.back() << "\n";
}

int main() {
  Fast_as_duck;

  /*
      #ifndef ONLINE_JUDGE
          freopen("input.txt", "r", stdin);
          freopen("output.txt", "w", stdout);
      #endif
  */
  int t = 1;

  // cin >> t;

  while (t--) {
    solve();
  }

  return 0;
}


Fixed submission:
// It doesn't matter as long as you rise to the top - Katsuki Bakugo
#include <bits/stdc++.h>
using namespace std;

#define Fast_as_duck                                                           \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.tie(0)
#define pb push_back
#define forn(i, st, n) for (int i = st; i < n; i++)
#define rev(i, st, n) for (int i = st; i >= n; i--)
#define ss second
#define ff first
#define ll long long

typedef pair<int, int> pii;

const int N = 1e5 + 10, mod = 1000000007;

int visited[2 * N];

void dfs(std::vector<int> path[], int u, int val, int visited[]) {
  visited[u] = val;
  // cout << u << " " << visited[u] << "\n";
  forn(i, 0, (int)path[u].size()) {
    if (visited[path[u][i]] == 0) {
      dfs(path, path[u][i], val, visited);
    }
  }
}

void solve() {

  int n, m;
  cin >> n >> m;

  std::vector<int> frnd[n + 1];
  int x, y;
  forn(i, 0, m) {
    cin >> x >> y;
    frnd[x].pb(y);
    frnd[y].pb(x);
  }

  // cout << "ans from here\n\n\n";

  // std::vector<int> visited(n+1 , 0);
  int val = 0;

  forn(i, 0, n) {
    if (visited[i + 1] == 0) {

      val++;
      visited[i + 1] = val;
      // cout << "dfs " << val << "\n";
      dfs(frnd, i + 1, val, visited);
    }
  }

  std::vector<int> ans(val + 1, 0);

  forn(i, 1, n + 1) {
    // cout << visited[i] << " ";
    ans[visited[i]]++;
  }

  sort(ans.begin(), ans.end());

  cout << ans.back() << "\n";
}

int main() {
  Fast_as_duck;

  /*
      #ifndef ONLINE_JUDGE
          freopen("input.txt", "r", stdin);
          freopen("output.txt", "w", stdout);
      #endif
  */
  int t = 1;

  // cin >> t;

  while (t--) {
    solve();
  }

  return 0;
}