Language: C++

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

#define ll long long
#define int long long
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define mod 1000000007
#define inf (int)(1e18)
#define ps(x, y) fixed << setprecision(y) << x
#define w(x)  \
    int x;    \
    cin >> x; \
    while (x--)
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define all(p) p.begin(), p.end()
#define ub(a, b) upper_bound(all(a), b)
#define lb(a, b) lower_bound(all(a), b)
#define sz(x) (int)x.size()
#define PI 3.14159265
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

void run()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
}
const int N = (int)(3e5);
vi parent(N, -1);
vi size(N, 0);
int find_set(int v)
{
    if (v == parent[v])
        return v;
    return parent[v] = find_set(parent[v]);
}
void make_set(int v)
{
    parent[v] = v;
    size[v] = 1;
}

void union_sets(int a, int b)
{
    a = find_set(a);
    b = find_set(b);
    if (a != b)
    {
        if (size[a] < size[b])
            swap(a, b);
        parent[b] = a;
        size[a] += size[b];
    }
}
void solution()
{
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        make_set(i);
    }
    int ans = 1;
    for (int i = 0; i < m; i++)
    {
        int u, v;
        cin >> u >> v;
        union_sets(u, v);
        ans = max({ans, size[find_set(u)], size[find_set(v)]});
    }
    cout << ans << endl;
    return;
}
int32_t main()
{
    run();
    solution();
    return 0;
}

Compiler output:
a.cc: In function 'void make_set(long long int)':
a.cc:49:5: error: reference to 'size' is ambiguous
   49 |     size[v] = 1;
      |     ^~~~
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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc: In function 'void union_sets(long long int, long long int)':
a.cc:58:13: error: reference to 'size' is ambiguous
   58 |         if (size[a] < size[b])
      |             ^~~~
/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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc:58:23: error: reference to 'size' is ambiguous
   58 |         if (size[a] < size[b])
      |                       ^~~~
/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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc:61:9: error: reference to 'size' is ambiguous
   61 |         size[a] += size[b];
      |         ^~~~
/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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc:61:20: error: reference to 'size' is ambiguous
   61 |         size[a] += size[b];
      |                    ^~~~
/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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc: In function 'void solution()':
a.cc:78:25: error: reference to 'size' is ambiguous
   78 |         ans = max({ans, size[find_set(u)], size[find_set(v)]});
      |                         ^~~~
/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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc:78:44: error: reference to 'size' is ambiguous
   78 |         ans = max({ans, size[find_set(u)], size[find_set(v)]});
      |                                            ^~~~
/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:39:4: note:                 'std::vector<long long int> size'
   39 | vi size(N, 0);
      |    ^~~~
a.cc:78:18: error: no matching function for call to 'max(<brace-enclosed initializer list>)'
   78 |         ans = max({ans, size[find_set(u)], size[find_set(v)]});
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 1 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   candidate expects 2 arguments, 1 provided