1var assert = require('assert');
2
3class MyLinkedList {
4  constructor() {
5    this.head = null;
6    this.tail = null;
7  }
8
9  prepend(newVal) {
10    const currentHead = this.head;
11    const newNode = new LinkedListNode(newVal);
12    newNode.next = currentHead;
13    this.head = newNode;
14
15    if (!this.tail) {
16      this.tail = newNode;
17    }
18  }
19
20  append(newVal) {
21    const newNode = new LinkedListNode(newVal);
22    if (!this.head) {
23      this.head = newNode;
24      this.tail = newNode;
25    } else {
26      this.tail.next = newNode;
27      this.tail = newNode;
28    }
29  }
30
31  toString() {
32    const toPrint = [];
33    let currNode = this.head;
34
35    while (currNode) {
36      toPrint.push(currNode.val);
37      currNode = currNode.next;
38    }
39
40    return toPrint.join(' -> ');
41  }
42}
43
44function Node(val) {
45  this.val = val;
46  this.next = null;
47}
48
49function LinkedListNode(val) {
50  this.val = val;
51  this.next = null;
52}
53
54var list1 = new LinkedListNode(3);
55var nodes1 = [4, 5, 6, 7, 8, 9, 10];
56createNodes(list1, nodes1);
57
58var list2 = new LinkedListNode(1);
59var nodes2 = [2, 3, 4, 5, 6, 7, 8];
60createNodes(list2, nodes2);
61
62function createNodes(head, nodes) {
63  for (let i = 0; i < nodes.length; i++) {
64    var newNode = new LinkedListNode(nodes[i]);
65    head.next = newNode;
66    head = newNode;
67  }
68}
69
70try {
71  var linkedList1 = new MyLinkedList();
72  linkedList1.prepend(25);
73  linkedList1.prepend(15);
74  linkedList1.prepend(5);
75  linkedList1.prepend(9);
76
77  assert.deepEqual(listToString(linkedList1.head), '9 -> 5 -> 15 -> 25');
78
79  console.log(
80    'PASSED: Calling #prepend on 25, 15, 5, and 9 should equal `9 -> 5 -> 15 -> 25`'
81  );
82} catch (err) {
83  console.log(err);
84}
85
86try {
87  var linkedList3 = new MyLinkedList();
88  linkedList3.prepend(25);
89  linkedList3.prepend(15);
90  linkedList3.prepend(5);
91  linkedList3.prepend(9);
92
93  linkedList3.append(15);
94  linkedList3.append(5);
95  linkedList3.append(9);
96
97  assert.deepEqual(
98    listToString(linkedList3.head),
99    '9 -> 5 -> 15 -> 25 -> 15 -> 5 -> 9'
100  );
101
102  console.log(
103    'PASSED: Calling #append on 15, 5, and 9 should equal `9 -> 5 -> 15 -> 25 -> 15 -> 5 -> 9`'
104  );
105} catch (err) {
106  console.log(err);
107}
108
109try {
110  var linkedList2 = new MyLinkedList();
111  linkedList2.prepend(15);
112  linkedList2.append(5);
113  linkedList2.prepend(7);
114  linkedList2.append(19);
115
116  assert.deepEqual(
117    listToString(linkedList2.head),
118    '7 -> 15 -> 5 -> 19',
119    "Prepending 15, appending 5, prepending 7, appending 19 should equal '7 -> 15 -> 5 -> 19'"
120  );
121
122  console.log(
123    'PASSED: Prepending 15, appending 5, prepending 7, appending 19 should equal `7 -> 15 -> 5 -> 19`'
124  );
125} catch (err) {
126  console.log(err);
127}
128
129function listToString(head) {
130  var toPrint = [];
131  var currNode = head;
132  while (currNode) {
133    toPrint.push(currNode.val);
134    currNode = currNode.next;
135  }
136  return toPrint.join(' -> ');
137}