1
var isRectangleCover = function (R) {
2
  // left to right, bottom to top (so sort on bottom first, then left)
3
  R.sort(
4
    ([left1, bottom1], [left2, bottom2]) => bottom1 - bottom2 || left1 - left2
5
  );
6

7
  // Find all corners
8
  let leftMost = Infinity,
9
    bottomMost = Infinity,
10
    rightMost = -Infinity,
11
    topMost = -Infinity;
12
  for (let [left, bottom, right, top] of R) {
13
    leftMost = Math.min(leftMost, left);
14
    bottomMost = Math.min(bottomMost, bottom);
15
    rightMost = Math.max(rightMost, right);
16
    topMost = Math.max(topMost, top);
17
  }
18

19
  // All calculations are with-respect-to large rectangle
20
  let CH = new Array(rightMost - leftMost).fill(0);
21
  for (let [left, bottom, right, top] of R) {
22
    const baseHeight = bottom - bottomMost; // how high base is
23
    const ceilHeight = top - bottomMost; // how high ceil is
24
    for (let tempLeft = left; tempLeft < right; tempLeft++) {
25
      if (CH[tempLeft - leftMost] != baseHeight) return false; // > is a duplicate cell < is a gap/ missing cell/ hole
26
      CH[tempLeft - leftMost] = ceilHeight;
27
    }
28
  }
29

30
  const rectHeight = topMost - bottomMost;
31
  for (let ceilHeight of CH) {
32
    if (ceilHeight !== rectHeight) return false;
33
  }
34
  return true;
35
};