Language: C++

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fast ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
const ll mod = 1e9+7;

ll size[(ll)2e5+10], parent[(ll)2e5+10];

ll find_set(ll x) {
	if(x == parent[x])
		return x;
	return parent[x] = find_set(parent[x]);
}

void union_set(ll x, ll y) {
	if(size[x] < size[y])
		swap(x,y);
	parent[y] = x;
	size[x] += size[y];
}

int main() {
	ll n,m;
	cin>>n>>m;
	ll x,y,i;
	for(i=1;i<=n;i++) {
		parent[i] = i;
		size[i] = 1;
	}
	for(i=0;i<m;i++) {
		cin>>x>>y;
		x = find_set(x);
		y = find_set(y);
		if(x != y) {
			union_set(x,y);
		}
	}
	ll mx=0;
	for(i=1;i<=n;i++)
		mx = max(mx, size[i]);
	cout<<mx;
	return 0;
}

Compiler output:
a.cc: In function 'void union_set(long long int, long long int)':
a.cc:16:12: error: reference to 'size' is ambiguous
   16 |         if(size[x] < size[y])
      |            ^~~~
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 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:7:4: note:                 'long long int size [200010]'
    7 | ll size[(ll)2e5+10], parent[(ll)2e5+10];
      |    ^~~~
a.cc:16:22: error: reference to 'size' is ambiguous
   16 |         if(size[x] < size[y])
      |                      ^~~~
/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:7:4: note:                 'long long int size [200010]'
    7 | ll size[(ll)2e5+10], parent[(ll)2e5+10];
      |    ^~~~
a.cc:19:9: error: reference to 'size' is ambiguous
   19 |         size[x] += size[y];
      |         ^~~~
/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:7:4: note:                 'long long int size [200010]'
    7 | ll size[(ll)2e5+10], parent[(ll)2e5+10];
      |    ^~~~
a.cc:19:20: error: reference to 'size' is ambiguous
   19 |         size[x] += size[y];
      |                    ^~~~
/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:7:4: note:                 'long long int size [200010]'
    7 | ll size[(ll)2e5+10], parent[(ll)2e5+10];
      |    ^~~~
a.cc: In function 'int main()':
a.cc:28:17: error: reference to 'size' is ambiguous
   28 |                 size[i] = 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:7:4: note:                 'long long int size [200010]'
    7 | ll size[(ll)2e5+10], parent[(ll)2e5+10];
      |    ^~~~
a.cc:40:30: error: reference to 'size' is ambiguous
   40 |                 mx = max(mx, size[i]);
      |                              ^~~~
/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:7:4: note:                 'long long int size [200010]'
    7 | ll size[(ll)2e5+10], parent[(ll)2e5+10];
      |    ^~~~