SMMR-063: Watch Men

#include <bits/stdc++.h>

using namespace std;
using lli = long long;
using pll = pair <lli, lli>;
const int N = 2e5;
const lli INF = 2e18;

int main(){


    int n;
    lli ans = 0;
    scanf("%d", &n);

    map <lli, int> same;
    vector <pll> point1, point2;
    for(int i=1;i<=n;i++){
        lli x, y;
        scanf("%lld%lld", &x, &y);
        same[y] ++;
        point1.push_back({x, y});
        point2.push_back({y, x});
    }

    sort(point1.begin(), point1.end());
    sort(point2.begin(), point2.end());

    lli prev = -INF;
    lli cnt = 0;
    for(auto p: point1){
        lli x, y;
        x = p.first;
        y = p.second;
        if(prev == -INF){
            prev = x;
            cnt = 1;
            continue;
        }
        if(prev == x){
            cnt ++;
        }
        else {
            if(cnt > 1) ans += (lli)(cnt)*(cnt-1) / 2;
            prev = x;
            cnt = 1;
        }
    }
    if(cnt > 1) ans += (lli)(cnt)*(cnt-1) / 2;

    lli prey = -INF, prex = -INF;
    cnt = 0;
    lli h = 1;
    vector <lli> X;
    for(auto p: point2){
        lli x, y;
        y = p.first;
        x = p.second;
        if(prey == -INF){
            prey = y;
            prex = x;
            cnt = 1;
            continue;
        }
        if(prey == y){
            if(prex == x) cnt ++;
            else {
                X.push_back(cnt);
                cnt = 1;
            }
        }
        else {
            X.push_back(cnt);
            int sz = X.size();
            for(int i=0;i<sz-1;i++){
                for(int j=i+1;j<sz;j++){
                    ans += (lli) X[i]*X[j];
                }
            }
            if(sz != 0) X.clear();
            cnt = 1;
        }
        prex = x;
        prey = y;
    }

    X.push_back(cnt);
    int sz = X.size();
    for(int i=0;i<sz-1;i++){
        for(int j=i+1;j<sz;j++){
            ans += (lli) X[i]*X[j];
        }
    }

    printf("%lld", ans);

    return 0;
}
/**

4
1 2
1 2
1 3
4 2

3
1 1
7 5
1 5

6
0 0
0 1
0 2
-1 1
0 1
1 1

7
1 2
1 2
1 2
1 3
1 3
4 2
4 2

**/