C.cpp

// dile a la jardinera que traigo flores
// corner cases // int vs ll // cin vs scanf
#include <bits/stdc++.h>
#define ff first
#define ss second
#define mp make_pair
#define pb push_back
#define sz(x) int(x.size())
#define fill(x,v) memset(x,v,sizeof(x))
#define FER(i,a,b) for(int i = int(a); i < int(b); ++i)
#define trace(x) cout << #x << " = " << x << endl
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;

vector< vector<int> > dots;
map<int,vector<int> > mapa;

int check(int id, int x1, int x2){
    auto it = lower_bound(dots[id].begin(),dots[id].end(),x1);
    if(it == dots[id].end()) return 0;
    int val = *it;
    it++;
    if(val == x1 and it != dots[id].end() and *it == x2) return 1;
    if(val > x2) return 0;
    return -1;
}

int main(){

    fastio;
    int n,x,y;
    cin >> n;
    FER(i,0,n){
        cin >> x >> y;
        mapa[y].pb(x);
    }

    int c = 0;
    dots.resize(sz(mapa));
    for(auto &par : mapa){
        dots[c] = par.second;
        sort(dots[c].begin(),dots[c].end());
        c++;
    }

    int ans = 0;
    for(int i = 0; i < sz(dots); ++i){
        for(int j = 0; j < sz(dots[i])-1; ++j){
            int x1 = dots[i][j], x2 = dots[i][j+1];
            for(int k = i-1; k >= 0; --k){
                int res = check(k,x1,x2);
                if(res == 1) ans++;
                if(res == 1 or res == -1) break;
            }
            for(int k = i+1; k < sz(dots); ++k){
                int res = check(k,x1,x2);
                if(res == 1) ans++;
                if(res == 1 or res == -1) break;
            }
        }
    }
    cout << ans/2 << endl;
    return 0;
}