Language: C++

#include<iostream>
#include<string>
#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<deque>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
using namespace std;

typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf=1e9+7;
const ll INF=1LL<<60 ;
const ll mod=1e9+7 ;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(),c.end()
#define pb push_back
#define debug(x)  cout << #x << " = " << (x) << endl;
using Graph = vector<vector<int> >;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
//#define int long long

struct UnionFind {
    vector<int> par, w;
    
    UnionFind(int n) : par(n, -1), w(n, 0) { }
    void init(int n) { par.assign(n, -1); w.assign(n, 0); }
    
    int root(int x) {
        if (par[x] < 0) return x;
        else return par[x] = root(par[x]);
    }
    
    bool issame(int x, int y) {
        return root(x) == root(y);
    }
    
    bool merge(int x, int y) {
        x = root(x); y = root(y);
        if (x == y) {
            ++w[x];
            return false;
        }
        if (par[x] > par[y]) swap(x, y); // merge technique
        par[x] += par[y];
        par[y] = x;
        w[x] += w[y];
        ++w[x];
        return true;
    }
    
    int size(int x) {
        return -par[root(x)];
    }
 
    int wei(int x) {
        return w[root(x)];
    }
};

//密グラフのMSTは考えるべき辺の本数を減らす
//MST　は　O(ElogV)

void solve() {
	int n; cin >> n;
    vector<ll> x(n), y(n);
    rep(i, n) cin >> x[i] >> y[i];

    using edge = pair<ll, LP>;
    vector<edge> edges;

    vector<int> ids(n);
    iota(all(ids), 0);
    sort(all(ids), [&](int i, int j){ return x[i] > y[j];});
    rep(i, n - 1) {
        int u = ids[i], v = ids[i+1];
        edges.push_back(edge(x[u] - x[v], LP(u, v)));
    }

    sort(all(ids), [&](int i, int j){ return y[i] > y[j];});
    rep(i, n - 1) {
        int u = ids[i], v = ids[i+1];
        edges.push_back(edge(y[u] - y[v], LP(u, v)));
    }

    sort(all(edges));
    UnionFind uf(n);
    ll res = 0;
    for(auto e: edges) {
        int u = e.sc.fr, v = e.sc.sc;
        ll cost = e.fr.fr;
        if(uf.issame(u, v)) continue;
        uf.merge(u, v);
        res += cost;
    }
    cout << res << endl;
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//init();
	solve();
	//cout << "finish" << endl;
    return 0;
}

Compiler output:
a.cc: In function 'void solve()':
a.cc:43:12: error: request for member 'first' in 'e.std::pair<long long int, std::pair<long long int, long long int> >::first', which is of non-class type 'long long int'
   43 | #define fr first
      |            ^~~~~
a.cc:121:24: note: in expansion of macro 'fr'
  121 |         ll cost = e.fr.fr;
      |                        ^~