// Valid Square
class Solution {
  int d(vector<int>& p, vector<int>& q) {
    return (p[0]-q[0])*(p[0]-q[0])+(p[1]-q[1])*(p[1]-q[1]);
  }
public:
  bool validSquare(vector<int>& p1, vector<int>& p2, vector<int>& p3, vector<int>& p4) {
    unordered_set<int> s{d(p1,p2), d(p1,p3), d(p1,p4), d(p2,p3), d(p2,p4), d(p3,p4)};
    return ! s.count(0) && s.size() == 2;
  }
};