Language: C++

#include <iostream>
#include <fstream>
#include <set>
#include <map>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <functional>
#include <algorithm>
#include <climits>
#include <cmath>
#include <iomanip>
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000
const int MAX_N = 100010;

int par[MAX_N];
int Rank[MAX_N];
int size;

void init(int n) {
    for (int i = 0; i < n; i++) {
        par[i] = i;
        Rank[i] = 0;
    }
    size = n;
}

int find(int x) {
    if (par[x] == x) {
        return x;
    } else {
        return par[x] = find(par[x]);
    }
}

void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return;

    size--;
    if (Rank[x] < Rank[y]) {
        par[x] = y;
    } else {
        par[y] = x;
        if (Rank[x] == Rank[y]) {
            Rank[x]++;
        }
    }
}
bool same(int x, int y) {
    return find(x) == find(y);
}

int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, M;
    
    cin >> N >> M;
    init(N);
    rep(i, M) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        unite(a, b);
    }
    cout << size - 1 << endl;

    return 0;
}


Compiler output:
a.cc: In function 'void init(int)':
a.cc:36:5: error: reference to 'size' is ambiguous
   36 |     size = n;
      |     ^~~~
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:29:5: note:                 'int size'
   29 | int size;
      |     ^~~~
a.cc: In function 'void unite(int, int)':
a.cc:52:5: error: reference to 'size' is ambiguous
   52 |     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:29:5: note:                 'int size'
   29 | int size;
      |     ^~~~
a.cc: In function 'int main()':
a.cc:80:13: error: reference to 'size' is ambiguous
   80 |     cout << size - 1 << endl;
      |             ^~~~
/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:29:5: note:                 'int size'
   29 | int size;
      |     ^~~~