题解如下

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

long long count_right_triangles(vector<pair<int, int>>& points) {
unordered_map<int, int> x_freq;
unordered_map<int, int> y_freq;

// 分别统计 x 和 y 坐标的频率
for (auto& point : points) {
    x_freq[point.first]++;
    y_freq[point.second]++;
}

// 对于每个点，使用 x 和 y 的频率来计算三角形的数量
long long count = 0;
for (auto& point : points) {
    count += (long long)(x_freq[point.first] - 1) * (y_freq[point.second] - 1);
}

return count;

}

int main() {
int N;
cin >> N;

vector<pair<int, int>> points(N);
for (int i = 0; i < N; ++i) {
    cin >> points[i].first >> points[i].second;
}

cout << count_right_triangles(points) << endl;
return 0;

}