layout	title
page	Jungle Beat

Before You Begin

We're going to do some silly things with sound and linked lists. Let's make a drum machine that's backed by a linked list.

Making Sound

Go into your Terminal and try this:

$ say -r 500 -v Boing "ding, dah, oom, oom, ding, oom, oom, oom, ding, dah, oom, oom, ding, dah, oom, oom, ding, dah, oom, oom "

Yeah. That's what we're looking for. Now try it from Ruby:

$ pry
> `say -r 500 -v Boing "ding, dah, oom, oom"`

Note that the backticks allow you to run terminal commands from within Ruby.

Linked Lists

Linked Lists are one of the most fundamental Computer Science data structures. A Linked List models a collection of data as a series of "nodes" which link to one another in a chain.

In a singly-linked list (the type we will be building) you have a head, which is a node representing the "start" of the list, and subsequent nodes which make up the remainder of the list.

The list itself can hold a reference to one thing -- the head node.

Each node can hold a single element of data and a link to the next node in the list.

The last node of the list is often called its tail.

Using sweet ASCII art, it might look like this:

List -- (head) --> ["hello" | -]-- (link) --> ["world" | -]-- (link) --> ["!" | ]

The three nodes here hold the data "hello", "world", and "!". The first two nodes have links which point to other nodes. The last node, holding the data "!", has no reference in the link spot. This signifies that it is the end of the list.

Learning Goals / Areas of Focus

• Practice breaking a program into logical components
• Distinguishing between classes and instances of those classes
• Understanding how linked lists work to store and find data
• Testing components in isolation and in combination

Base Expectations

Then we'll exercise the functionality from a Pry session:

require "./lib/jungle_beat"
> jb = JungleBeat.new("deep dep dep deep")
> jb.play
=> 4 # also plays the sounds
> jb.append("deep bop bop deep")
=> 4
> jb.all
=> "deep dep dep deep deep bop bop deep"
> jb.prepend("tee tee tee tee")
=> 4 # number of beats inserted
> jb.all
=> "tee tee tee tee deep dep dep deep deep bop bop deep"
> jb.include?("dep")
=> true
> jb.pop(4)
=> "deep bop bop deep"
> jb.all
=> "tee tee tee tee deep dep dep deep"
> jb.count
=> 8
> jb.insert(4, "boop bop bop boop")
=> "tee tee tee tee boop bop bop boop deep dep dep deep"
> jb.find(8, 2)
=> "deep dep"

Internal Structure

You must use a Linked List to store your beats. Each node should contain only a single "word"/beat. You'll want to implement at least each of the following features for your list:

• append an element to the end of the list
• prepend an element at the beginning of the list
• insert one or more elements at an arbitrary position in the list
• includes? gives back true or false whether the supplied value is in the list
• pop one or more elements from the end of the list
• count the number of elements in the list
• find one or more elements based on arbitrary positions in the list. The first parameter indicates the first position to return and the second parameter specifies how many elements to return.
• all return all elements in the linked list in order

Extensions

1. Validating Beats

There are a lot of words which aren't going to work for beats. Like Mississippi.

Add validation to your program such that the input beats must be members of your defined list. Insertion of a beat not in the list is rejected. Like this:

> jb = JungleBeat.new("deep")
> jb.append("Mississippi")
=> 0
> jb.all
=> "deep"
> jb.prepend("tee tee tee Mississippi")
=> 3 # number of beats successfully inserted
> jb.all
=> "tee tee tee deep"

Here's a starter list of valid beats, but add more if you like:

tee dee deep bop boop la na

2. Speed & Voice

Let's make it so the user can control the voice and speed of playback. Originally we showed you to use say -r 500 -v Boing where r is the rate and v is the voice. Let's setup a usage like this:

> jb = JungleBeat.new("deep dop dop deep")
> jb.play
=> 4 # plays the four sounds normal speed with Boing voice
> jb.rate = 100
=> 100
> jb.play
=> 4 # plays the four sounds slower with Boing voice
> jb.voice = "Alice"
=> "Alice"
> jb.play
=> 4 # plays the four sounds slower with Alice voice
> jb.reset_rate
=> 500
> jb.reset_voice
=> "Boing"
> jb.play
=> 4 # plays the four sounds normal speed with Boing voice

Tips

• A linked list it not an array. While it may perform many of the same functions as an array, its structure is conceptually very different.
• There are only 3 types of "state" that need to be tracked for a linked list -- the head of the list, the data of each node, and the "next node" of each node.
• In object-oriented programming, "state" is generally modeled with instance variables
• There are two main ways to implement Linked Lists: iteration and recursion. Iterative solutions use looping structures (while, for) to walk through the nodes in the list. Recursive solutions use methods which call themselves to walk through nodes. It would be ideal to solve it each way.
• Most of your methods will be defined on the List itself, but you will need to manipulate one or more Nodes to implement them.
• TDD will be your friend in implementing the list. Remember to start small, work iteratively, and test all of your methods.
• An empty list has nil as its head
• The tail of a list is the node that has nil as its next node

Constraints

• Make sure that your code is well tested for both expected cases and edge cases. Try popping more elements than there are in the list. Try seeing if an empty list includes anything. Try inserting elements at a position beyond the length of the list. That kind of thing.
• Avoid using other ruby collections (Arrays, Hashes, etc) for the storage of your beats. That's where you're supposed to use the linked list. But having Arrays elsewhere in your code, or using methods that return arrays (like .split) are totally ok.

Resources

Need some help on Linked Lists? You can check out some of the following resources:

• https://www.youtube.com/watch?v=oiW79L8VYXk
• http://www.eternallyconfuzzled.com/tuts/datastructures/jsw_tut_linklist.aspx
• http://www.cs.cmu.edu/~adamchik/15-121/lectures/Linked%20Lists/linked%20lists.html
• http://www.sitepoint.com/rubys-missing-data-structure/

Evaluation Rubric

The project will be assessed with the following rubric:

1. Functional Expectations

• 4: Application fulfills all base expectations and the one extension
• 3: Application fulfills all base expectations
• 2: Application is missing one base expectation
• 1: Application is missing more than one base expectation

2. Test-Driven Development

• 4: Application is broken into components which are well tested in both isolation and integration using appropriate data
• 3: Application is well tested but does not balance isolation and integration tests, using only the data necessary to test the functionality
• 2: Application makes some use of tests, but the coverage is insufficient
• 1: Application does not demonstrate strong use of TDD

3. Encapsulation / Breaking Logic into Components

• 4: Application is expertly divided into logical components each with a clear, single responsibility
• 3: Application effectively breaks logical components apart but breaks the principle of SRP
• 2: Application shows some effort to break logic into components, but the divisions are inconsistent or unclear
• 1: Application logic shows poor decomposition with too much logic mashed together

4. Fundamental Ruby & Style

• 4: Application demonstrates excellent knowledge of Ruby syntax, style, and refactoring
• 3: Application shows strong effort towards organization, content, and refactoring
• 2: Application runs but the code has long methods, unnecessary or poorly named variables, and needs significant refactoring
• 1: Application generates syntax error or crashes during execution

5. Looping or Recursion

• 4: Application makes excellent use of loop/recursion techniques
• 3: Application makes effective use of loop/recursion techniques
• 2: Application has issues with loop/recursion techniques or mixes them inappropriately
• 1: Application struggles to loop/recurse at all