Posts Tagged With "Programming"

Sorting: Average-case Lower Bounds...

Bobby posted in Computer Science | Jun 02, 2023

Are you back or are you new here? If you're back, why'd you even come back? If you're new, you are in for hell. People who are back, you know what's coming. People who are new, you don't know what's coming. But you will. You will. Last time, we discussed "Why Comparison-based Sorting Algorithms have $\Omega(n log n)$ Lower Bound" and this is a follow-up to that. Also, if you haven't read that, go read the previous article first, then come back here and read this. Alright, ready? Let's go.

Today, we will discuss average-case lower bounds for comparison-based sorting algorithms. Now, I don't expect your little brain to remember everything you were spoon-fed last time, so I'll give you a quick recap. As expected, our focus in this article, once again, is comparison-based sorting Algorithms. In our last article, we were able to define a comparison-based sorting algorithm.

Also, we were able to prove that any comparison-based sorting algorithm must take $\Omega(n log n)$ time in the worst case. And, we also defined a theorem for this proof. Do you remember what it was? Of course, you don't. Here's the theorem:

Continue Reading | 1 Comment Computer Science 💻 Programming Data Structures Algorithms 🧬

Multi View Interfaces in Bubble Tea

Bobby posted in Programming | Feb 14, 2024

Recently, I was trying to build a "multi-screen" or "multi-view" application in Go using the Bubble Tea library. Now, for those who don't know, Bubble Tea is a framework for building terminal-based UIs/applications which is based on The Elm Architecture. Not only this, Bubble Tea also ships with a lot of "sister" libraries which can be used to further enhance your experience of building CLI or TUI applications with Bubble Tea. Bubbles and Lip Gloss are two such libraries which are built on top of Bubble Tea and which I am also using through this article.

Now, back to the basic problem. All I wanted to do was to switch between two (or potentially more) screens. So, let's start by building two example screens — one with a spinner and the other with a simple text message. But before we do that, let's first see how The Elm Architecture works. Right here, you can see picture of the Elm Architecture which I stole from the official Elm guide. The Elm Architecture is based on three main components:

Continue Reading | 5 Comments Computer Science 💻 Programming Insights

Packrat Parsing and Parsing Expression Grammars

Bobby posted in Computer Science | Nov 24, 2023

One of the most important features of the Parsing Expression Grammar formalism is that it is packrat parsable. This means that it can be parsed in linear time using a technique called memoization. This technique is also known as tabling in the logic programming community. The basic idea of a Parsing Expression Grammar or PEG is that you have a DSL or a domain specific language which looks exactly like a BNF, except that it is a program and its a parser. Now, these PEGs can be ambiguous and are capable of backtracking. Packrat parsers make the backtracking efficient with caching. How this works, is that the parser remembers the results of all the sub-parsers it has already run, and if it encounters the same sub-parser again, it just returns the result from the previous run. This behaviour makes packrat parsing is a very powerful technique.

When you design a language you typically want to formalize the syntax with a context-free grammar and then you feed it through a compiler and it'll generate a table-driven, bottom-up parser. Then you may have to hack on the grammar until you get it right because in order for the parsers to be efficient they need to be able to look ahead just one symbol so that they know what choice to make as they typically don't support backtracking. Of course there are versions which support infinite backtracking, but that can make your parser very inefficient. So, usually what you try to do in order to get a very efficient parser is you try and turn it into a nice grammar and then you use the generated parser to do what you like.

Continue Reading | 1 Comment Computer Science 💻 Programming Theory of Computation

Building a Simple User Presence

Bobby posted in Programming | Jun 04, 2023

Guess who's back? Back again?... for the rest, go listen to the fucking song! I am not here to sing songs for you. Anyroad, what's up? Actually, no one cares... so, let's get started! Remember back in the day, when you visited your favourite forum and it would say something like "$N$ users online: $(n)$ members, $(x)$ guests" (of course $ {n, x} \in \mathbb{N} $)? This is called user presence. It's a simple way to show your users that they are not alone on your website. It's also a great way to show off your mad skills to your friends. So, let's get started!

Before we start, I would like to discuss your options to track user presence on your website. There are multiple ways to do this:

WebSockets: This is the most modern and probably the most efficient way to do this. WebSockets will provide you with a persistent, bidirectional communication channel between your server and the client. Talking in a broad perspective, you would set up a WebSocket server that listens for incoming connections and handles WebSocket events, and when a client establishes a WebSocket connection, register their presence by storing relevant data (e.g., user ID, session ID) on the server. Then you can implement mechanisms to track user activity, such as sending heartbeats or receiving client-initiated events. 

Continue Reading | 3 Comments Computer Science 💻 Programming

Why Sorting has n(log n) Lower Bound?

Bobby posted in Computer Science | May 27, 2023

Alright, folks! I know I keep this weblog very personal and there's art flowing all around this website, but let's talk some mathematics today! Specifically, we are here to discuss the notion of lower bounds for sorting algorithms. Now, when I say sorting algorithms, I am talking about comparison-based sorting algorithms. There are other sorting algorithms like counting sort, radix sort, bucket sort, etc. but they are a topic for another day. Now, buckle up for a long text-based post and a vomit load of mathematics, because, by the end of this article, we are going to show that any deterministic comparison-based sorting algorithm must take $\Omega(n \log n)$ time to sort an array of n elements in the worst case.

You started reading this article, and reached this point and wondered, "Wait, we are discussing the notion of lower bounds"? "What is a lower bound"? ... "To think that, what the fuck even is a bound"? Well, if you are pondering over that question, well ponder no more! I promised you a shit-ton of information and a butt-load of theory, so here we go!

Continue Reading | 3 Comments Computer Science 💻 Programming Data Structures Algorithms 🧬