Merge pull request #20 from ulasaydin/master

Added Reverse Linked List Problem.

Author: ashokdey

README.md

@@ -17,6 +17,7 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
   - [N Element From Last](src/_DataStructures_/LinkedList/element-from-last)
   - [Middle Node](src/_DataStructures_/LinkedList/middle-node)
   - [Detect Loop](src/_DataStructures_/LinkedList/loop-in-list)
+  - [Reverse Linked List](src/_DataStructures_/LinkedList/reverse-linked-list)
 - [Stack](src/_DataStructures_/Stack)
   - [Implement Queue Using Stack](src/_DataStructures_/Stack/immitate-queue-using-stack)
   - [Baseball Game](src/_DataStructures_/Stack/baseball-game)

src/_DataStructures_/LinkedList/reverse-linked-list/index.js

@@ -0,0 +1,15 @@
+function reverseLinkedList(linkedList) {
+    let next = linkedList.getFirst();
+    let current = null;
+    let prev;
+    while(next != null){
+        prev = current;
+        current = next;
+        next = next.next;
+        current.next = prev;
+    }
+    return current;
+};
+module.exports = {
+    reverseLinkedList,
+  };

src/_DataStructures_/LinkedList/reverse-linked-list/reverse-linked-list.test.js

@@ -0,0 +1,37 @@
+const { LinkedList } = require('../index');
+const { reverseLinkedList } = require('.');
+
+describe('Reverse a LinkedList', () => {
+  let list = null;
+  beforeEach(() => {
+    list = new LinkedList();
+    list.addAtBeginning('1');
+    list.addAtEnd('2');
+    list.addAtEnd('3');
+    list.addAtEnd('4');
+    list.addAtEnd('5');
+  });
+
+  it('Should return `null` for empty list', () => {
+    list.delete();
+    expect(reverseLinkedList(list)).toEqual(null);
+  });
+
+  it('Should return `5`->`4`->`3`->`2`->`1` for the given list', () => {
+    let reversedList = reverseLinkedList(list);
+    expect(reversedList.data).toEqual('5');
+    expect(reversedList.next.data).toEqual('4');
+    expect(reversedList.next.next.data).toEqual('3');
+    expect(reversedList.next.next.next.data).toEqual('2');
+    expect(reversedList.next.next.next.next.data).toEqual('1');
+  });
+
+  it('Should return `3`->`2`->`1` after deleting 2 last nodes of the list', () => {
+    list.removeFromEnd();
+    list.removeFromEnd();
+    let reversedList2 = reverseLinkedList(list);
+    expect(reversedList2.data).toEqual('3');
+    expect(reversedList2.next.data).toEqual('2');
+    expect(reversedList2.next.next.data).toEqual('1');
+  });
+});