source-code/Valid_Square.cpp

class Solution {
    #define X first
    #define Y second
    
    long d(vector<int>& p1, vector<int>& p2) {
        return (p1[0] - p2[0]) * (p1[0] - p2[0]) + (p1[1] - p2[1]) * (p1[1] - p2[1]);
    }
public:
    bool validSquare(vector<int>& p1, vector<int>& p2, vector<int>& p3, vector<int>& p4) {
        unordered_set<long> lengthSet{ d(p1, p2), d(p1, p3), d(p1, p4), d(p2, p3), d(p2, p4), d(p3, p4) };
        return !lengthSet.count(0) and lengthSet.size() == 2;
    }
};