Create 3625. Count Number of Trapezoids II

3625. Count Number of Trapezoids II

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+class Solution {
+public:
+    int countTrapezoids(vector<vector<int>>& points) {
+        int n = points.size();
+        int INF = 1e9 + 7;
+        unordered_map<float , vector<float>> slopeToIntercept;
+        unordered_map<int , vector<float>> midToSlope;
+        int res = 0;
+
+        for (int i = 0; i < n; i++) {
+            int x1 = points[i][0];
+            int y1 = points[i][1];
+            for (int j = i + 1; j < n; j++) {
+                int x2 = points[j][0];
+                int y2 = points[j][1];
+                int dx = x1 - x2;
+                int dy = y1 - y2;
+
+                float k , b;
+                if (x2 == x1) {
+                    k = INF;
+                    b = x1;
+                }
+                else {
+                    k = (float)(y2 - y1) / (x2 - x1);
+                    b = (float)(y1 * dx - x1 * dy) / dx;
+                }
+
+                int mid = (x1 + x2) * 10000 + (y1 + y2);
+                slopeToIntercept[k].push_back(b);
+                midToSlope[mid].push_back(k);
+            }
+        }
+
+        for (auto& [_ , sti] : slopeToIntercept) {
+            if (sti.size() == 1) continue;
+
+            map<float , int> count;
+            for (float b : sti) count[b]++; 
+
+            int sum = 0;
+            for (auto& [_ , cnt] : count) {
+                res += (sum * cnt);
+                sum += cnt;
+            }
+        }
+
+        for (auto& [_ , mts] : midToSlope) {
+            if (mts.size() == 1) continue;
+
+            map<float , int> count;
+            for (float k : mts) count[k]++;
+
+            int sum = 0;
+            for (auto& [_ , cnt] : count) {
+                res -= (sum * cnt);
+                sum += cnt;
+            }
+        }
+        return res;
+    }
+};