NPException / scramblies

This repository contains my solutions to the following tasks:

Task 1

Complete the function (scramble str1 str2) that returns true if a portion of str1 characters can be rearranged to match str2, otherwise returns false

Notes:

• Only lower case letters will be used (a-z). No punctuation or digits will be included.
• Performance needs to be considered

Examples:

(scramble? “rekqodlw” ”world') ==> true
(scramble? “cedewaraaossoqqyt” ”codewars”) ==> true
(scramble? “katas”  “steak”) ==> false

Task 2

Create a web service that accepts two strings in a request and applies function scramble? from previous task to them.

Task 3

Create a UI in ClojureScript with two inputs for strings and a scramble button. When the button is fired it should call the API from previous task and display a result.

How to run

To start the web server from Task 2, execute lein run.
This will start the server on port 8080.

To open the ClojureScript UI from Task 3, execute lein fig.
This will start figwheel on port 9500 and open the browser.

Approach & Thoughts

Task 1

At first I just wanted to make a set for both input strings and then check if the second set is contained in the first. This would have passed the 3 given test cases, but does not match the specification since it won't account for multiple occurences of the same character.

Which brought me to my current implementation:
Count the available characters in the first string via the frequencies function.
Then iterate through the second string while checking if enough characters are left in the map.

I chose to convert the available-characters map to a transient, in order to make updating the map more performant. It doesn't really make a difference for smaller input sizes, but saves some time for larger inputs.

I have also added another possible implementation in the scramblies.experiment namespace, which is a lot quicker. But to achieve that I reimplemented frequencies with a regular Java HashMap. Benchmarking results are at the bottom of that namespace.

[Edit] After talking about the challenge with a friend, he decided to implement the function in Rust as an excercise. He was using a BitSet to keep track of the characters of the first String that had already been used. I was curious how fast the equivalent code in Clojure would be, so I added it as a third implementation and added benchmark results in the namespace as well.

Task 2

I decided to use Jetty as a server, with a combination of reitit and some Ring middleware to do the routing and request/response parsing.

This piece of code contains the routing logic, input and output validation, as well as parameter coercion, as provided by reitit.

I added a small middleware function to create a basic error response for requests which don't go to the right endpoint or don't use the right HTTP method.

Last but not least, starting the server is just passing the router and additional middleware to the Ring Jetty adapter.

Task 3

This was an interesting task, since I had not done anything with ClojureScript before.
I had heard of Figwheel and re-frame before, so I decided to start my CS journey with those. I looked up some getting started guides for both, and built my UI by iterating on some example code until it did what I wanted. In order to have something that is not just plain HTML, I used mvp.css.

The final UI consists of the HTML skeleton and some ClojureScript code.

I was surprised how little code there was in the end. Some setup code aside, there's basically just the event listener which does the API call, and the main render code.

One major thing that could be improved is to properly handle error responses from the API, and give the user better feedback for it.