1
var generateTrees = function (n) {
2
  if (n <= 0) {
3
    return [];
4
  }
5
  return generateRec(1, n);
6
};
7

8
function generateRec(start, end) {
9
  let result = [];
10

11
  if (start > end) {
12
    result.push(null);
13
    return result;
14
  }
15

16
  for (let i = start; i < end + 1; i++) {
17
    let left = generateRec(start, i - 1);
18
    let right = generateRec(i + 1, end);
19

20
    for (let l = 0; l < left.length; l++) {
21
      for (let r = 0; r < right.length; r++) {
22
        let root = new TreeNode(i, left[l], right[r]);
23
        result.push(root);
24
      }
25
    }
26
  }
27
  return result;
28
}