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