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

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define ll long long
#define int long long // comment it out when MLE
#define endl "\\n"
// template <typename T>
// using ordered_set = tree<T, null_type, less<int>, rb_tree_tag,
// tree_order_statistics_node_update>;

#define gok                                                                    \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
// # define m 163577857
#define mo 1000000007
#define pi acos(-1)
#define fi first
#define se second
#define pb push_back
#define pii pair<int, int>
#define REP(i, n) for (int i = 1; i <= n; i++)
const ll mod = 1e9 + 7;
// const int K = 2;
// typedef vector<vector<int> > matrix;
/*
       int add(int a, int b,int mod) {
             a%=mod;
             b%=mod;
             a += b;
             if (a >= mod) a -= mod;
             if(a<0)
             {
                 a += mod;
                 a %= mod;
             }
             return a;
         }

         int mul(ll a, int b,int mod) {
             a%=mod;
             b%=mod;
             a *= b;
             a += mod;
             return a % mod;
         }
         int po(int a,int b,int mod)
         {
             if(b==0)
                 return 1;
             if(b%2==0)
                 return po(mul(a,a,mod),b/2,mod);
             return mul(a,po(mul(a,a,mod),(b-1)/2,mod),mod);
         }


         ll fact[200003];
         ll inv[200003];

         void fact0()
         {
             int i,j;
             fact[0]=1;
             for(i=1;i<=200000;i++)
             {
                 fact[i]=i*fact[i-1]%mod;
             }
             inv[0]=1;
             inv[1]=1;
             ll p=mod;
             for (i=2; i<=200000; i++)
                 inv[i] = (p - (p/i) * inv[p%i] % p) % p;

             for(i=2;i<=200000;i++)
             {
                 inv[i]*=inv[i-1];
                 inv[i]%=mod;
             }
         }
         int help(int a,int b)
         {
            // cout<<a<<" "<<b<<endl;
             int an = fact[a];
             //cout<<an<<endl;
             an *= inv[b];
             an %= mod;
             an *= inv[a-b];
             an %= mod;
             return an;
         }
/*
       void random()
         {
           srand(time(0));
         for (int i = 0; i < n; i ++)
             perm[i] = i + 1;
         random_shuffle(perm, perm + n);
         }

int ncr(int a,int b)
{
 if(b>a)
     return 0;
 int tt = fact[a];
 tt %= mod;
 tt *= inv[a-b];
 tt %= mod;
 tt *= inv[b];
 tt %= mod;
 return tt;
}
*/
/*
struct tri{
    tri *arr[2];
};

tri *newNode()
{
    tri *temp = new tri;
    //temp->value = 0;
    temp->arr[0] = temp->arr[1] = NULL;
    return temp;
}
void insert(tri *root,int val)
{
    tri *temp = root;
    for (int i=32; i>=0; i--)
    {
        bool idx = ((val&(1ll<<i)));
       // cout<<idx<<" ";
        if(temp->arr[idx]==NULL)
        {
            temp->arr[idx] = newNode();
        }
        temp = temp->arr[idx];
    }
   //cout<<endl;
}
int qry(tri *root,int val)
{
    int an=0;
    tri *temp = root;
    for (int i=32; i>=0; i--)
    {
        if((val&(1LL<<i))>0)
        {
            if(temp->arr[0]!=NULL){
            temp = temp->arr[0];
            an += (1LL<<i);
           // cout<<(1ll<<i)<<" ";
            }
            else if(temp->arr[1]!=NULL)
                temp=temp->arr[1];
            else{

                break;
            }
        }
        else
        {
          if(temp->arr[1]!=NULL){
            temp = temp->arr[1];
            an += (1LL<<i);
           // cout<<(1ll<<i)<<" ";

            }
            else if(temp->arr[0]!=NULL)
                temp=temp->arr[0];
            else{
                 break;
            }
        }
    }
    //cout<<endl;
    return an;
}
*/
int n, m;
vector<int> v[200005];
bool vis[200005] = {false};
int dfs(int x) {
  vis[x] = true;
  int cnt = 1;
  for (auto ii : v[x]) {
    if (!vis[ii]) {
      cnt += dfs(ii);
    }
  }
  return cnt;
}
signed main() {
  gok

          cin >>
      n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    v[x].pb(y);
    v[y].pb(x);
  }

  int ma = 0;
  for (int i = 1; i <= n; i++) {
    if (!vis[i]) {
      ma = max(ma, dfs(i));
    }
  }

  cout << ma;

  return 0;
}


Error: WA

Fixed submission:

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define ll long long
#define int long long // comment it out when MLE
#define endl "\\n"
// template <typename T>
// using ordered_set = tree<T, null_type, less<int>, rb_tree_tag,
// tree_order_statistics_node_update>;

#define gok                                                                    \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
// # define m 163577857
#define mo 1000000007
#define pi acos(-1)
#define fi first
#define se second
#define pb push_back
#define pii pair<int, int>
#define REP(i, n) for (int i = 1; i <= n; i++)
const ll mod = 1e9 + 7;
// const int K = 2;
// typedef vector<vector<int> > matrix;
/*
       int add(int a, int b,int mod) {
             a%=mod;
             b%=mod;
             a += b;
             if (a >= mod) a -= mod;
             if(a<0)
             {
                 a += mod;
                 a %= mod;
             }
             return a;
         }

         int mul(ll a, int b,int mod) {
             a%=mod;
             b%=mod;
             a *= b;
             a += mod;
             return a % mod;
         }
         int po(int a,int b,int mod)
         {
             if(b==0)
                 return 1;
             if(b%2==0)
                 return po(mul(a,a,mod),b/2,mod);
             return mul(a,po(mul(a,a,mod),(b-1)/2,mod),mod);
         }


         ll fact[200003];
         ll inv[200003];

         void fact0()
         {
             int i,j;
             fact[0]=1;
             for(i=1;i<=200000;i++)
             {
                 fact[i]=i*fact[i-1]%mod;
             }
             inv[0]=1;
             inv[1]=1;
             ll p=mod;
             for (i=2; i<=200000; i++)
                 inv[i] = (p - (p/i) * inv[p%i] % p) % p;

             for(i=2;i<=200000;i++)
             {
                 inv[i]*=inv[i-1];
                 inv[i]%=mod;
             }
         }
         int help(int a,int b)
         {
            // cout<<a<<" "<<b<<endl;
             int an = fact[a];
             //cout<<an<<endl;
             an *= inv[b];
             an %= mod;
             an *= inv[a-b];
             an %= mod;
             return an;
         }
/*
       void random()
         {
           srand(time(0));
         for (int i = 0; i < n; i ++)
             perm[i] = i + 1;
         random_shuffle(perm, perm + n);
         }

int ncr(int a,int b)
{
 if(b>a)
     return 0;
 int tt = fact[a];
 tt %= mod;
 tt *= inv[a-b];
 tt %= mod;
 tt *= inv[b];
 tt %= mod;
 return tt;
}
*/
/*
struct tri{
    tri *arr[2];
};

tri *newNode()
{
    tri *temp = new tri;
    //temp->value = 0;
    temp->arr[0] = temp->arr[1] = NULL;
    return temp;
}
void insert(tri *root,int val)
{
    tri *temp = root;
    for (int i=32; i>=0; i--)
    {
        bool idx = ((val&(1ll<<i)));
       // cout<<idx<<" ";
        if(temp->arr[idx]==NULL)
        {
            temp->arr[idx] = newNode();
        }
        temp = temp->arr[idx];
    }
   //cout<<endl;
}
int qry(tri *root,int val)
{
    int an=0;
    tri *temp = root;
    for (int i=32; i>=0; i--)
    {
        if((val&(1LL<<i))>0)
        {
            if(temp->arr[0]!=NULL){
            temp = temp->arr[0];
            an += (1LL<<i);
           // cout<<(1ll<<i)<<" ";
            }
            else if(temp->arr[1]!=NULL)
                temp=temp->arr[1];
            else{

                break;
            }
        }
        else
        {
          if(temp->arr[1]!=NULL){
            temp = temp->arr[1];
            an += (1LL<<i);
           // cout<<(1ll<<i)<<" ";

            }
            else if(temp->arr[0]!=NULL)
                temp=temp->arr[0];
            else{
                 break;
            }
        }
    }
    //cout<<endl;
    return an;
}
*/
int n, m;
vector<int> v[200005];
bool vis[100005] = {false};
int dfs(int x) {
  vis[x] = true;
  int cnt = 1;
  for (auto ii : v[x]) {
    if (!vis[ii]) {
      cnt += dfs(ii);
    }
  }
  return cnt;
}
signed main() {
  gok

          cin >>
      n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    v[x].pb(y);
    v[y].pb(x);
  }

  int ma = 0;
  for (int i = 1; i <= n; i++) {
    if (!vis[i]) {
      ma = max(ma, dfs(1));
    }
  }

  cout << ma;

  return 0;
}