Add solution #3531

JoshCrozier · JoshCrozier · commit 2701caf365f4 · 2025-12-11T20:56:48.000-06:00
diff --git a/README.md b/README.md
@@ -2782,6 +2782,7 @@
 3512|[Minimum Operations to Make Array Sum Divisible by K](./solutions/3512-minimum-operations-to-make-array-sum-divisible-by-k.js)|Easy|
 3516|[Find Closest Person](./solutions/3516-find-closest-person.js)|Easy|
 3520|[Minimum Threshold for Inversion Pairs Count](./solutions/3520-minimum-threshold-for-inversion-pairs-count.js)|Medium|
+3531|[Count Covered Buildings](./solutions/3531-count-covered-buildings.js)|Medium|
 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|
diff --git a/solutions/3531-count-covered-buildings.js b/solutions/3531-count-covered-buildings.js
@@ -0,0 +1,52 @@
+/**
+ * 3531. Count Covered Buildings
+ * https://leetcode.com/problems/count-covered-buildings/
+ * Difficulty: Medium
+ *
+ * You are given a positive integer n, representing an n x n city. You are also given
+ * a 2D grid buildings, where buildings[i] = [x, y] denotes a unique building located
+ * at coordinates [x, y].
+ *
+ * A building is covered if there is at least one building in all four directions:
+ * left, right, above, and below.
+ *
+ * Return the number of covered buildings.
+ */
+
+/**
+ * @param {number} n
+ * @param {number[][]} buildings
+ * @return {number}
+ */
+var countCoveredBuildings = function(n, buildings) {
+  const rowBuildings = new Map();
+  const colBuildings = new Map();
+  let result = 0;
+
+  for (const [x, y] of buildings) {
+    if (!rowBuildings.has(x)) rowBuildings.set(x, []);
+    if (!colBuildings.has(y)) colBuildings.set(y, []);
+    rowBuildings.get(x).push(y);
+    colBuildings.get(y).push(x);
+  }
+  for (const coords of rowBuildings.values()) {
+    coords.sort((a, b) => a - b);
+  }
+  for (const coords of colBuildings.values()) {
+    coords.sort((a, b) => a - b);
+  }
+  for (const [x, y] of buildings) {
+    const rowCoords = rowBuildings.get(x);
+    const colCoords = colBuildings.get(y);
+    const hasLeft = rowCoords[0] < y;
+    const hasRight = rowCoords[rowCoords.length - 1] > y;
+    const hasAbove = colCoords[0] < x;
+    const hasBelow = colCoords[colCoords.length - 1] > x;
+
+    if (hasLeft && hasRight && hasAbove && hasBelow) {
+      result++;
+    }
+  }
+
+  return result;
+};
