Problem p02573 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define ld long double

#define rep(i, a, b) for (int i = a; i < b; i++)
#define repb(i, a, b) for (int i = a; i > b; i--)

#define pb push_back
#define mp make_pair
#define all(A) A.begin(), A.end()
#define allr(A) A.rbegin(), A.rend()
#define precise(i) fixed << setprecision(i)
#define fi first
#define se second

#define err() cout << "\\n==================================\\n";
#define errA(A)                                                                \\
  for (auto i : A)                                                             \\
    cout << i << " ";                                                          \\
  cout << "\\n";
#define err1(a) cout << #a << " " << a << "\\n";
#define err2(a, b) cout << #a << " " << a << " " << #b << " " << b << "\\n";
#define err3(a, b, c)                                                          \\
  cout << #a << " " << a << " " << #b << " " << b << " " << #c << " " << c     \\
       << "\\n";
#define err4(a, b, c, d)                                                       \\
  cout << #a << " " << a << " " << #b << " " << b << " " << #c << " " << c     \\
       << " " << #d << " " << d << "\\n";

const int logN = 20;
const int M = 1000000007;
const int INF = 1e12;
#define PI 3.14159265;
const int N = 200005;

#define Pii pair<int, int>
#define Vi vector<int>
#define Vpii vector<Pii>

Vi adj[200001];
vector<bool> visited(200001, false);
int ma = 0;
set<Pii> al;

void dfs(int s, int &sum) {
  if (visited[s]) {
    return;
  }
  visited[s] = true;
  sum++;
  for (auto u : adj[s]) {
    dfs(u, sum);
  }
}

void solve() {
  int n, m;
  cin >> n >> m;
  rep(c, 0, m) {
    int x, y;
    cin >> x >> y;
    if (al.count(mp(x, y))) {
      continue;
    }
    adj[x].pb(y);
    adj[y].pb(x);
    al.insert(mp(x, y));
    al.insert(mp(y, x));
  }
  rep(c, 1, n + 1) {
    if (visited[c]) {
      continue;
    }
    int sum = 0;
    dfs(c, sum);
    ma = max(ma, sum);
  }
  cout << ma;
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  //    cin>>t;
  while (t--) {
    solve();
  }
  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define ld long double

#define rep(i, a, b) for (int i = a; i < b; i++)
#define repb(i, a, b) for (int i = a; i > b; i--)

#define pb push_back
#define mp make_pair
#define all(A) A.begin(), A.end()
#define allr(A) A.rbegin(), A.rend()
#define precise(i) fixed << setprecision(i)
#define fi first
#define se second

#define err() cout << "\\n==================================\\n";
#define errA(A)                                                                \\
  for (auto i : A)                                                             \\
    cout << i << " ";                                                          \\
  cout << "\\n";
#define err1(a) cout << #a << " " << a << "\\n";
#define err2(a, b) cout << #a << " " << a << " " << #b << " " << b << "\\n";
#define err3(a, b, c)                                                          \\
  cout << #a << " " << a << " " << #b << " " << b << " " << #c << " " << c     \\
       << "\\n";
#define err4(a, b, c, d)                                                       \\
  cout << #a << " " << a << " " << #b << " " << b << " " << #c << " " << c     \\
       << " " << #d << " " << d << "\\n";

const int logN = 20;
const int M = 1000000007;
const int INF = 1e12;
#define PI 3.14159265;
const int N = 200005;

#define Pii pair<int, int>
#define Vi vector<int>
#define Vpii vector<Pii>

Vi adj[200001];
vector<bool> visited(200001, false);
int ma = 0;

void dfs(int s, int &sum) {
  if (visited[s]) {
    return;
  }
  visited[s] = true;
  sum++;
  for (auto u : adj[s]) {
    dfs(u, sum);
  }
}

void solve() {
  int n, m;
  cin >> n >> m;
  rep(c, 0, m) {
    int x, y;
    cin >> x >> y;
    if (count(all(adj[x]), y)) {
      continue;
    }
    adj[x].pb(y);
    adj[y].pb(x);
  }
  rep(c, 1, n + 1) {
    if (visited[c]) {
      continue;
    }
    int sum = 0;
    dfs(c, sum);
    ma = max(ma, sum);
  }
  cout << ma;
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  //    cin>>t;
  while (t--) {
    solve();
  }
  return 0;
}