593

class Solution {
public:
    // helper function to calculate distance between two points
    int dist(vector<int>& p1, vector<int>& p2) {
        return (p2[0] - p1[0]) * (p2[0] - p1[0]) + (p2[1] - p1[1]) * (p2[1] - p1[1]);
    }

    bool validSquare(vector<int>& p1, vector<int>& p2, vector<int>& p3, vector<int>& p4) {
        // keep points in an array to be able to get them by index
        vector<vector<int>> points = {p1, p2, p3, p4};
        set<int> lengths;

        for (int i=0; i<4; i++) {
            for (int j=i+1; j<4; j++) {
                int curr = dist(points[i], points[j]);
                if (curr != 0)
                    lengths.insert(curr);

                // if distance is zero - we got a duplicated point
                else
                    return false;
            }
        }
        // We are supposed to end with only two different lengths: the sides and the diagonals
        return lengths.size() == 2;
    }
};