1var assert = require('assert');
2
3function isValidBST(root) {
4  const searchResults = [];
5  inOrder(root, searchResults);
6
7  for (let i = 1; i < searchResults.length; i++) {
8    if (searchResults[i - 1] >= searchResults[i]) {
9      return false;
10    }
11  }
12
13  return true;
14}
15
16function inOrder(root, output) {
17  if (!root) {
18    return;
19  }
20
21  inOrder(root.left, output);
22  output.push(root.val);
23  inOrder(root.right, output);
24}
25
26function Node(val) {
27  this.val = val;
28  this.left = null;
29  this.right = null;
30}
31
32// Regular binary trees
33var tree1 = new Node(4);
34tree1.left = new Node(1);
35tree1.right = new Node(3);
36
37var tree2 = new Node(5);
38tree2.left = new Node(10);
39tree2.left.left = new Node(17);
40tree2.left.right = new Node(3);
41tree2.right = new Node(8);
42
43// Binary search trees
44var tree3 = new Node(6);
45tree3.left = new Node(3);
46
47var tree4 = new Node(5);
48tree4.left = new Node(3);
49tree4.left.left = new Node(2);
50tree4.left.left.left = new Node(1);
51
52var tree5 = new Node(8);
53tree5.left = new Node(6);
54tree5.right = new Node(9);
55tree5.left.left = new Node(5);
56tree5.left.right = new Node(7);
57tree5.right.right = new Node(10);
58
59try {
60  assertIsFunction(isValidBST, '`isValidBST` is a function');
61
62  console.log('PASSED: ' + '`isValidBST` is a function');
63} catch (err) {
64  console.log(err);
65}
66
67try {
68  assert.equal(isValidBST(tree1), false);
69
70  console.log('PASSED: ' + '`isValidBST(tree1)` should return `false`');
71} catch (err) {
72  console.log(err);
73}
74
75try {
76  assert.equal(isValidBST(tree3), true);
77
78  console.log('PASSED: ' + '`isValidBST(tree3)` should return `true`');
79} catch (err) {
80  console.log(err);
81}
82
83function assertIsFunction(f) {
84  return typeof f === 'function';
85}