Add simple-linked-list (#334)

Author: BNAndras

config.json

@@ -698,6 +698,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 8
+      },
+      {
+        "slug": "simple-linked-list",
+        "name": "Simple Linked List",
+        "uuid": "1c96f455-f1d5-4aa1-950c-6e60fc2b09ae",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
       }
     ]
   },

exercises/practice/simple-linked-list/.docs/instructions.md

@@ -0,0 +1,19 @@
+# Instructions
+
+Write a prototype of the music player application.
+
+For the prototype, each song will simply be represented by a number.
+Given a range of numbers (the song IDs), create a singly linked list.
+
+Given a singly linked list, you should be able to reverse the list to play the songs in the opposite order.
+
+~~~~exercism/note
+The linked list is a fundamental data structure in computer science, often used in the implementation of other data structures.
+
+The simplest kind of linked list is a **singly** linked list.
+That means that each element (or "node") contains data, along with something that points to the next node in the list.
+
+If you want to dig deeper into linked lists, check out [this article][intro-linked-list] that explains it using nice drawings.
+
+[intro-linked-list]: https://medium.com/basecs/whats-a-linked-list-anyway-part-1-d8b7e6508b9d
+~~~~

exercises/practice/simple-linked-list/.docs/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+You work for a music streaming company.
+
+You've been tasked with creating a playlist feature for your music player application.

exercises/practice/simple-linked-list/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "simple-linked-list.coffee"
+    ],
+    "test": [
+      "simple-linked-list.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "Write a simple linked list implementation that uses Elements and a List.",
+  "source": "Inspired by 'Data Structures and Algorithms with Object-Oriented Design Patterns in Ruby', singly linked-lists.",
+  "source_url": "https://web.archive.org/web/20160731005714/http://brpreiss.com/books/opus8/html/page96.html"
+}

exercises/practice/simple-linked-list/.meta/example.coffee

@@ -0,0 +1,40 @@
+class Element
+  constructor: (@value, @next = null) ->
+
+class LinkedList
+  constructor: (values) ->
+    @count = 0
+    @head = null
+    if values?
+      for value in values
+        @add new Element value
+
+  length: ->
+    @count
+
+  add: (element) ->
+    elt = element
+    elt.next = @head
+    @head = elt
+    @count += 1
+
+  toArray: ->
+    elements = []
+    element = @head
+    while element?
+      elements.push element.value
+      element = element.next
+    elements
+
+  reverse: (prev = null) ->
+    if @head?.next
+      current = @head
+      @head = @head.next
+      current.next = prev
+      @reverse current
+    else
+      @head.next = prev
+    @
+
+module.exports.Element = Element
+module.exports.LinkedList = LinkedList

exercises/practice/simple-linked-list/simple-linked-list.coffee

@@ -0,0 +1,16 @@
+class Element
+  constructor: (value) ->
+
+class LinkedList
+  constructor: (values) ->
+
+  length: ->
+
+  add: (element) ->
+
+  toArray: ->
+
+  reverse: ->
+
+module.exports.Element = Element
+module.exports.LinkedList = LinkedList

exercises/practice/simple-linked-list/simple-linked-list.spec.coffee

@@ -0,0 +1,117 @@
+{ Element, LinkedList } = require './simple-linked-list'
+
+describe 'Simple Linked List', ->
+  describe 'Element class', ->
+    xit 'has constructor', ->
+      element = new Element 1
+      expect(element.value).toEqual 1
+
+    xit 'value reflects constructor arg', ->
+      element = new Element 2
+      expect(element.value).toEqual 2
+
+    xit 'has null for next by default', ->
+      element = new Element 1
+      expect(element.next).toEqual null
+    
+  describe 'List class', ->
+    xit 'has constructor', ->
+      list = new LinkedList
+      expect(list).toBeDefined()
+
+    xit 'new lists should have length 0', ->
+      list = new LinkedList
+      expect(list.length()).toEqual 0
+
+    xit 'can add a element', ->
+      list = new LinkedList
+      element = new Element 1
+      expect -> list.add element
+      .not.toThrow()
+
+    xit 'adding a element increments length', ->
+      list = new LinkedList
+      element = new Element 1
+      list.add element
+      expect(list.length()).toEqual 1
+
+    xit 'adding two elements increments twice', ->
+      list = new LinkedList
+      element1 = new Element 1
+      element2 = new Element 3
+      list.add element1
+      list.add element2
+      expect(list.length()).toEqual 2
+
+    xit 'new Lists have a null head element', ->
+      list = new LinkedList
+      expect(list.head).toEqual null
+
+    xit 'adding an Element to an empty list sets the head Element', ->
+      list = new LinkedList
+      element = new Element 1
+      list.add element
+      expect(list.head.value).toEqual 1
+
+    xit 'adding a second Element updates the head Element', ->
+      list = new LinkedList
+      element1 = new Element 1
+      element2 = new Element 3
+      list.add element1
+      list.add element2
+      expect(list.head.value).toEqual 3
+
+    xit 'can get the next Element from the head', ->
+      list = new LinkedList
+      element1 = new Element 1
+      element2 = new Element 3
+      list.add element1
+      list.add element2
+      expect(list.head.next.value).toEqual 1
+
+    xit 'can be inxitialized wxith an array', ->
+      list = new LinkedList [1, 2, 3]
+      expect(list.length()).toEqual 3
+      expect(list.head.value).toEqual 3
+
+  describe 'Lists wxith multiple elements', ->
+
+    xit 'wxith correct length', ->
+      list = new LinkedList [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+      expect(list.length()).toEqual 10
+
+    xit 'wxith correct head value', ->
+      list = new LinkedList [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
+      expect(list.head.value).toEqual 10
+
+    xit 'can traverse the list', ->
+      list = new LinkedList [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
+      expect(list.head.next.next.next.value).toEqual 7
+
+    xit 'can convert to an array', ->
+      list = new LinkedList [1]
+      expect(list.toArray()).toEqual [1]
+
+    xit 'head of list is final element from input array', ->
+      list = new LinkedList [1, 2]
+      expect(list.head.value).toEqual 2
+    
+    xit 'can convert longer list to an array', ->
+      list = new LinkedList [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
+      expect(list.toArray()).toEqual [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
+
+    xit 'can be reversed', ->
+      list = new LinkedList [1, 2]
+      expect(list.reverse().toArray()).toEqual [1, 2]
+
+    xit 'can be reversed when xit has more elements', ->
+      list = new LinkedList [1, 2, 3]
+      expect(list.reverse().toArray()).toEqual [1, 2, 3]
+
+    xit 'can reverse with many elements', ->
+      list = new LinkedList [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
+      expect(list.reverse().toArray()).toEqual [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+
+    xit 'can reverse a reversal', ->
+      list = new LinkedList [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
+      expect(list.reverse().reverse().toArray()).toEqual [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]