Rectangle Mania

• Time : O(n^2)
• Space : O(n)

#include <vector>

using namespace std;

int intersection(vector<int>& A, vector<int>& B) {
	int res = 0, i = 0, j = 0;
	while(i < A.size() and j < B.size()) {
		if(A[i] == B[j]) {
			res++,i++,j++;
		} else if(A[i] < B[j]) {
			i++;
		} else {
			j++;
		}
	}
	return res;
}

int rectangleMania(vector<vector<int>> coords) {
  unordered_map<int, vector<int>> mp;
	int res = 0;
	for(auto& coord: coords) {
		mp[coord[0]].push_back(coord[1]);
	}
	for(auto& [_, xaxis] : mp) {
		sort(begin(xaxis), end(xaxis));
	}
	for(auto i = begin(mp); i != end(mp); i++) {
		for(auto j = next(i); j != end(mp); j++) {
			int intersectCount = intersection(i->second, j->second);
			res += (intersectCount) * (intersectCount - 1) / 2;
		}
	}
  return res;
}