1class BTNode {
2  constructor(value) {
3    this.value = value;
4    this.left = null;
5    this.right = null;
6  }
7}
8
9/**
10 *
11 * @param {BTNode} tree
12 * @returns {Boolean}
13 */
14const isBinarySearchTree = (tree) => {
15  if (tree) {
16    if (
17      tree.left &&
18      (tree.left.value > tree.value || !isBinarySearchTree(tree.left))
19    ) {
20      return false;
21    }
22    if (
23      tree.right &&
24      (tree.right.value <= tree.value || !isBinarySearchTree(tree.right))
25    ) {
26      return false;
27    }
28  }
29  return true;
30};

11    def checkBST(t) 
22        return false if t==nil
33       if t.left!=nil && t.left>t 
44            return false
55        end
66        if t.right!=nil && t.right<t
77            return false
88        end
99        if checkBST(t.left) && checkBST(t.right)
1010            return true
1111        end
1212    end
13