Language: C++

#include<iostream>
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define N 2*10e5
#define precise cout<<fixed<<setprecision(10)
#pragma GCC optimize("O0")
#pragma GCC optimize ("Ofast")
#pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize ("-ffloat-store")
#define rep(i,a,b) for(int i=a;i<b;i++)
#define min3(a,b,c) min(a,min(b,c))
#define nl cout<<"\n";
#define all(v) v.begin(),v.end()
#define F first
#define S second
#define mod 1000000007
typedef long long ll;
typedef vector<long long> vl;
typedef vector<pair<long,long>> vp;
void get(ll arr[],ll n){for(ll i=0;i<n;i++) cin>>arr[i];}
ll gcd(ll a,ll b);
ll binpow(ll a,ll b);
set<ll> s[200001];
ll vis[200001]={0};
ll n,m,size=0;
void dfs(ll i)
{
    vis[i]=1;
    size++;
    for(auto &x: s[i])
    {
        if(vis[x]==0) dfs(x);
    }
}
void solve()
{
    ll n,m;
    cin>>n>>m;
    ll a,b;
    rep(i,0,m)
    {
        cin>>a>>b;
        s[a].insert(b);
        s[b].insert(a);
    }
    set<ll> v;
    rep(i,1,n+1)
    {
        if(vis[i]==0)
        {
            size=0;
            dfs(i);
            v.insert(size);
        }
    }
    auto it=v.end();
    it--;
    cout<<*it;
}
int main()
{
 	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	ll t;
	t=1;
	//cin>>t;
	while(t--)
	{
	 	solve();
	}
	//cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n";
}
ll binpow(ll a, ll b) {
   ll res = 1;
    while (b > 0) {
        if (b & 1)
            res = res * a;
        a = a * a;
        b >>= 1;
    }
    return res;
}
ll gcd(ll a,ll b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

Compiler output:
a.cc: In function 'void dfs(ll)':
a.cc:31:5: error: reference to 'size' is ambiguous
   31 |     size++;
      |     ^~~~
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/range_access.h:272:5: note: candidates are: 'template<class _Tp, long unsigned int _Nm> constexpr std::size_t std::size(const _Tp (&)[_Nm])'
  272 |     size(const _Tp (&)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note:                 'template<class _Container> constexpr decltype (__cont.size()) std::size(const _Container&)'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc:27:8: note:                 'll size'
   27 | ll n,m,size=0;
      |        ^~~~
a.cc: In function 'void solve()':
a.cc:53:13: error: reference to 'size' is ambiguous
   53 |             size=0;
      |             ^~~~
/usr/include/c++/14/bits/range_access.h:272:5: note: candidates are: 'template<class _Tp, long unsigned int _Nm> constexpr std::size_t std::size(const _Tp (&)[_Nm])'
  272 |     size(const _Tp (&)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note:                 'template<class _Container> constexpr decltype (__cont.size()) std::size(const _Container&)'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc:27:8: note:                 'll size'
   27 | ll n,m,size=0;
      |        ^~~~
a.cc:55:22: error: reference to 'size' is ambiguous
   55 |             v.insert(size);
      |                      ^~~~
/usr/include/c++/14/bits/range_access.h:272:5: note: candidates are: 'template<class _Tp, long unsigned int _Nm> constexpr std::size_t std::size(const _Tp (&)[_Nm])'
  272 |     size(const _Tp (&)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note:                 'template<class _Container> constexpr decltype (__cont.size()) std::size(const _Container&)'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc:27:8: note:                 'll size'
   27 | ll n,m,size=0;
      |        ^~~~