Add solution #2001

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,679 LeetCode solutions in JavaScript
+# 1,680 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1535,6 +1535,7 @@
 1997|[First Day Where You Have Been in All the Rooms](./solutions/1997-first-day-where-you-have-been-in-all-the-rooms.js)|Medium|
 1998|[GCD Sort of an Array](./solutions/1998-gcd-sort-of-an-array.js)|Hard|
 2000|[Reverse Prefix of Word](./solutions/2000-reverse-prefix-of-word.js)|Easy|
+2001|[Number of Pairs of Interchangeable Rectangles](./solutions/2001-number-of-pairs-of-interchangeable-rectangles.js)|Medium|
 2011|[Final Value of Variable After Performing Operations](./solutions/2011-final-value-of-variable-after-performing-operations.js)|Easy|
 2016|[Maximum Difference Between Increasing Elements](./solutions/2016-maximum-difference-between-increasing-elements.js)|Easy|
 2017|[Grid Game](./solutions/2017-grid-game.js)|Medium|

solutions/2001-number-of-pairs-of-interchangeable-rectangles.js

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+/**
+ * 2001. Number of Pairs of Interchangeable Rectangles
+ * https://leetcode.com/problems/number-of-pairs-of-interchangeable-rectangles/
+ * Difficulty: Medium
+ *
+ * You are given n rectangles represented by a 0-indexed 2D integer array rectangles,
+ * where rectangles[i] = [widthi, heighti] denotes the width and height of the ith rectangle.
+ *
+ * Two rectangles i and j (i < j) are considered interchangeable if they have the same
+ * width-to-height ratio. More formally, two rectangles are interchangeable if
+ * widthi/heighti == widthj/heightj (using decimal division, not integer division).
+ *
+ * Return the number of pairs of interchangeable rectangles in rectangles.
+ */
+
+/**
+ * @param {number[][]} rectangles
+ * @return {number}
+ */
+var interchangeableRectangles = function(rectangles) {
+  const map = new Map();
+  let result = 0;
+
+  for (const [width, height] of rectangles) {
+    const gcd = (a, b) => b === 0 ? a : gcd(b, a % b);
+    const divisor = gcd(width, height);
+    const ratio = `${width / divisor}/${height / divisor}`;
+
+    if (map.has(ratio)) {
+      result += map.get(ratio);
+      map.set(ratio, map.get(ratio) + 1);
+    } else {
+      map.set(ratio, 1);
+    }
+  }
+
+  return result;
+};