Add solution #3623

JoshCrozier · JoshCrozier · commit 525affe06568 · 2025-12-02T09:30:49.000-06:00
diff --git a/README.md b/README.md
@@ -2784,6 +2784,7 @@
 3535|[Unit Conversion II](./solutions/3535-unit-conversion-ii.js)|Medium|
 3539|[Find Sum of Array Product of Magical Sequences](./solutions/3539-find-sum-of-array-product-of-magical-sequences.js)|Hard|
 3541|[Find Most Frequent Vowel and Consonant](./solutions/3541-find-most-frequent-vowel-and-consonant.js)|Easy|
+3623|[Count Number of Trapezoids I](./solutions/3623-count-number-of-trapezoids-i.js)|Medium|
 
 ## License
 
diff --git a/solutions/3623-count-number-of-trapezoids-i.js b/solutions/3623-count-number-of-trapezoids-i.js
@@ -0,0 +1,40 @@
+/**
+ * 3623. Count Number of Trapezoids I
+ * https://leetcode.com/problems/count-number-of-trapezoids-i/
+ * Difficulty: Medium
+ *
+ * You are given a 2D integer array points, where points[i] = [xi, yi] represents the
+ * coordinates of the ith point on the Cartesian plane.
+ *
+ * A horizontal trapezoid is a convex quadrilateral with at least one pair of horizontal
+ * sides (i.e. parallel to the x-axis). Two lines are parallel if and only if they have
+ * the same slope.
+ *
+ * Return the number of unique horizontal trapezoids that can be formed by choosing any
+ * four distinct points from points.
+ *
+ * Since the answer may be very large, return it modulo 109 + 7.
+ */
+
+/**
+ * @param {number[][]} points
+ * @return {number}
+ */
+var countTrapezoids = function(points) {
+  const MOD = 1e9 + 7;
+
+  const map = new Map();
+  for (const [x, y] of points) {
+    map.set(y, (map.get(y) || 0) + 1);
+  }
+
+  let result = 0n;
+  let total = 0n;
+  for (const count of map.values()) {
+    const lines = BigInt(count) * BigInt(count - 1) / 2n;
+    result = (result + total * lines) % BigInt(MOD);
+    total = (total + lines) % BigInt(MOD);
+  }
+
+  return Number(result);
+};
