Add solution #2013

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,687 LeetCode solutions in JavaScript
+# 1,688 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1544,6 +1544,7 @@
 2009|[Minimum Number of Operations to Make Array Continuous](./solutions/2009-minimum-number-of-operations-to-make-array-continuous.js)|Hard|
 2011|[Final Value of Variable After Performing Operations](./solutions/2011-final-value-of-variable-after-performing-operations.js)|Easy|
 2012|[Sum of Beauty in the Array](./solutions/2012-sum-of-beauty-in-the-array.js)|Medium|
+2013|[Detect Squares](./solutions/2013-detect-squares.js)|Medium|
 2016|[Maximum Difference Between Increasing Elements](./solutions/2016-maximum-difference-between-increasing-elements.js)|Easy|
 2017|[Grid Game](./solutions/2017-grid-game.js)|Medium|
 2027|[Minimum Moves to Convert String](./solutions/2027-minimum-moves-to-convert-string.js)|Easy|

solutions/2013-detect-squares.js

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+/**
+ * 2013. Detect Squares
+ * https://leetcode.com/problems/detect-squares/
+ * Difficulty: Medium
+ *
+ * You are given a stream of points on the X-Y plane. Design an algorithm that:
+ * - Adds new points from the stream into a data structure. Duplicate points are allowed and should
+ *   be treated as different points.
+ * - Given a query point, counts the number of ways to choose three points from the data structure
+ *   such that the three points and the query point form an axis-aligned square with positive area.
+ *
+ * An axis-aligned square is a square whose edges are all the same length and are either parallel
+ * or perpendicular to the x-axis and y-axis.
+ *
+ * Implement the DetectSquares class:
+ * - DetectSquares() Initializes the object with an empty data structure.
+ * - void add(int[] point) Adds a new point point = [x, y] to the data structure.
+ * - int count(int[] point) Counts the number of ways to form axis-aligned squares with point
+ *   point = [x, y] as described above.
+ */
+
+var DetectSquares = function() {
+  this.points = new Map();
+};
+
+/**
+ * @param {number[]} point
+ * @return {void}
+ */
+DetectSquares.prototype.add = function(point) {
+  const [x, y] = point;
+  const key = `${x},${y}`;
+  this.points.set(key, (this.points.get(key) || 0) + 1);
+};
+
+/**
+ * @param {number[]} point
+ * @return {number}
+ */
+DetectSquares.prototype.count = function(point) {
+  const [x, y] = point;
+  let result = 0;
+
+  for (const [key, count] of this.points) {
+    const [px, py] = key.split(',').map(Number);
+    if (px === x || py === y || Math.abs(px - x) !== Math.abs(py - y)) continue;
+
+    const point1 = `${x},${py}`;
+    const point2 = `${px},${y}`;
+    result += count * (this.points.get(point1) || 0) * (this.points.get(point2) || 0);
+  }
+
+  return result;
+};