Sprint Challenge: Data Structures

In this week's Sprint you implemented some classic and fundamental data structures and learned about how to go about evaluating their respective runtimes and performance. This Sprint Challenge aims to assess your comfort with these topics through exercises that build on the data structures you implemented and the algorithmic intuition you've started to build up.

Instructions

Read these instructions carefully. Understand exactly what is expected before starting this Sprint Challenge.

This is an individual assessment. All work must be your own. Your Challenge score is a measure of your ability to work independently using the material covered throughout this sprint. You need to demonstrate proficiency in the concepts and objectives that were introduced and that you practiced in the preceding days.

You are not allowed to collaborate during the Sprint Challenge. However, you are encouraged to follow the twenty-minute rule and seek support from your TL and Instructor in your cohort help channel on Slack. Your submitted work reflects your proficiency in the concepts and topics that were covered this week.

You have three hours to complete this Sprint Challenge. Plan your time accordingly.

Commits

Commit your code regularly and meaningfully. This helps both you (in case you ever need to return to old code for any number of reasons) and it also helps your project manager to more thoroughly assess your work.

Description

This Sprint Challenge is split into three parts:

1. Implement a data structure called a ring buffer (more details below)
2. Optimizing some inefficient code
3. Reversing the contents of a singly linked list

Minimum Viable Product

Task 1. Implement a Ring Buffer Data Structure

A ring buffer is a non-growable buffer with a fixed size. When the ring buffer is full and a new element is inserted, the oldest element in the ring buffer is overwritten with the newest element. This kind of data structure is very useful for use cases such as storing logs and history information, where you typically want to store information up until it reaches a certain age, after which you don't care about it anymore and don't mind seeing it overwritten by newer data.

Implement this behavior in the RingBuffer class. RingBuffer has two methods, append and get. The append method adds the given element to the buffer. The get method returns all of the elements in the buffer in a list in their given order. It should not return any None values in the list even if they are present in the ring buffer.

For example:

buffer = RingBuffer(3)

buffer.get()   # should return []

buffer.append('a')
buffer.append('b')
buffer.append('c')

buffer.get()   # should return ['a', 'b', 'c']

# 'd' overwrites the oldest value in the ring buffer, which is 'a'
buffer.append('d')

buffer.get()   # should return ['d', 'b', 'c']

buffer.append('e')
buffer.append('f')

buffer.get()   # should return ['d', 'e', 'f']

Task 2. Runtime Optimization

!Important! If you are running this using PowerShell by clicking on the green play button, you will get an error that names1.txt is not found. To resolve this, run it, get the error, then cd into the names directory in the python terminal that opens in VSCode.

Navigate into the names directory. Here you will find two text files containing 10,000 names each, along with a program names.py that compares the two files and prints out duplicate name entries. Try running the code with python3 names.py. Be patient because it might take a while: approximately six seconds on my laptop. What is the runtime complexity of this code?

Six seconds is an eternity so you've been tasked with speeding up the code. Your goal is to use one of the data structures we built out over the course of this week in order to optimize and improve on the runtime so that it's more efficient than O(n²).

A follow-up question to think about: once you've used one of the data structures we implemented over the course of the week in order to improve the runtime of the implementation, what other data structures (including ones from Python's standard library) are also possible candidates for improving the runtime of the implementation?

Task 3. Reverse a Linked List

Inside of the reverse directory, you'll find a basic implementation of a Singly Linked List. Without making it a Doubly Linked List (adding a tail attribute), complete the reverse_list() function within reverse/reverse.py.

For example,

1->2->3->None

would become...

3->2->1->None

While credit will be given for a functional solution, only optimal solutions will earn a 3 on this task.

Stretch

• Say your code from names.py is to run on an embedded computer with very limited RAM. Because of this, memory is extremely constrained and you are only allowed to store names in arrays (i.e. Python lists). How would you go about optimizing the code under these conditions? Try it out and compare your solution to the original runtime. (If this solution is less efficient than your original solution, include both and label the strech solution with a comment)

Rubric

TASK	1 - DOES NOT MEET Expectations	2 - MEETS Expectations	3 - EXCEEDS Expectations	SCORE
Task 1. Implement a Ring Buffer Data Structure	Solution in ring_buffer.py DOES NOT run OR it runs but has multiple logical errors, failing 2 or more tests.	Solution in ring_buffer.py runs, but may have one or two logical errors; passes at least 5/6 tests (Note that each function in the test file that begins with test is a test).	Solution in ring_buffer.py has no syntax or logical errors and passes all tests (Note that each function in the test file that begins with test is a test).
Task 2. Runtime Optimization	Student does NOT correctly identify the runtime of the starter code in name.py and is not able to optimize it to run in under 6 seconds using a data structure that was implemented during the week.	Student does not identify the runtime of the starter code in name.py, but optimizes it to run in under 6 seconds, with a solution that exhibits the appropriate runtime, using a data structure that was implemented during the week	Student does BOTH correctly identify the runtime of the starter code in name.py and optimizes it to run in under 6 seconds, with an appropriate runtime using a data structure that was implemented during the week.
Task 3. Reverse the contents of a Singly Linked List	Student's solution in reverse.py is failing one or more tests.	Student's solution in reverse.py is able to correctly print out the contents of the Linked List in reverse order, passing all tests, BUT, the runtime of their solution is not optimal (requires looping through the list more than once).	Student's solution in reverse.py is able to correctly print out the contents of the Linked List in reverse order, passing all tests AND exhibits an appropriate runtime.

Passing the Sprint

Score ranges for a 1, 2, and 3 are shown in the rubric above. For a student to have passed a sprint challenge, they need to earn an at least 2 for all items on the rubric.