Add solution #391

Author: JoshCrozier

README.md

@@ -309,6 +309,7 @@
 388|[Longest Absolute File Path](./0388-longest-absolute-file-path.js)|Medium|
 389|[Find the Difference](./0389-find-the-difference.js)|Easy|
 390|[Elimination Game](./0390-elimination-game.js)|Medium|
+391|[Perfect Rectangle](./0391-perfect-rectangle.js)|Hard|
 392|[Is Subsequence](./0392-is-subsequence.js)|Easy|
 394|[Decode String](./0394-decode-string.js)|Medium|
 395|[Longest Substring with At Least K Repeating Characters](./0395-longest-substring-with-at-least-k-repeating-characters.js)|Medium|

solutions/0391-perfect-rectangle.js

@@ -0,0 +1,39 @@
+/**
+ * 391. Perfect Rectangle
+ * https://leetcode.com/problems/perfect-rectangle/
+ * Difficulty: Hard
+ *
+ * Given an array rectangles where rectangles[i] = [xi, yi, ai, bi] represents an axis-aligned
+ * rectangle. The bottom-left point of the rectangle is (xi, yi) and the top-right point of it
+ * is (ai, bi).
+ *
+ * Return true if all the rectangles together form an exact cover of a rectangular region.
+ */
+
+/**
+ * @param {number[][]} rectangles
+ * @return {boolean}
+ */
+var isRectangleCover = function(rectangles) {
+  const result = new Set();
+  let area = 0;
+  let minX = Infinity;
+  let maxX = -Infinity;
+  let minY = Infinity;
+  let maxY = -Infinity;
+
+  for (const [x1, y1, x2, y2] of rectangles) {
+    area += (x2 - x1) * (y2 - y1);
+    minX = Math.min(minX, x1);
+    minY = Math.min(minY, y1);
+    maxX = Math.max(maxX, x2);
+    maxY = Math.max(maxY, y2);
+    for (const corner of [`${x1},${y1}`, `${x2},${y1}`, `${x1},${y2}`, `${x2},${y2}`]) {
+      result.has(corner) ? result.delete(corner) : result.add(corner);
+    }
+  }
+
+  return area === (maxX - minX) * (maxY - minY) && result.size === 4
+    && result.has(`${minX},${minY}`) && result.has(`${maxX},${minY}`)
+    && result.has(`${minX},${maxY}`) && result.has(`${maxX},${maxY}`);
+};