Toptal Engineering Expert
Predicting Likes: Inside A Simple Recommendation Engine’s Algorithms
The Internet is becoming “smarter” every day. The video-sharing website that you frequently visit seems to know exactly what you will like, even before you have seen it. The online shopping cart holding your items almost magically figures out the one thing that you may have missed or intended to add before checking out. It’s as if these web services are reading your mind—or are they?
Turns out, predicting a user’s likes involves more math than magic. In this article we explore one of the many ways of building a recommendation engine that is both simple to implement and understand.

Mahmud Ridwan
Mahmud is a software developer with many years of experience and a knack for efficiency, scalability, and stable solutions.
Ruby Concurrency and Parallelism: A Practical Tutorial
A thorough and practical introduction to concurrent and parallel programming in Ruby, presenting and contrasting a number of techniques and options available, from the standpoints of both performance and complexity. Discusses forking, multithreading, the Global Interpreter Lock (GIL), and more.

Eqbal Quran
Eqbal is a senior full-stack developer with more than a decade of experience working in web and mobile development.
How GWT Unlocks Augmented Reality in Your Browser
In our previous post on the GWT Web Toolkit, we discussed the strengths and characteristics of GWT to mix Java and JavaScript libraries seamlessly in the browser. In today’s post, we would like to go a little deeper and see the GWT Toolkit in action. We’ll demonstrate how we can take advantage of GWT to build a peculiar application: an augmented reality web application that runs in real time, fully in JavaScript, in the browser. We’ll focus on how GWT gives us the ability to interact easily with many JavaScript APIs, such as WebRTC and WebGL, and allows us to harness a large Java library, NyARToolkit, never intended to be used in the browser.

Alberto Mancini
Alberto is a full-stack developer, ops engineer, and software architect with expertise managing large computational infrastructures. He has been a member of the Intel Software Innovator program since 2014 and holds a PhD in applied mathematics and operational research from the University of Milan.
How does Shazam work? Music Recognition Algorithms, Fingerprinting, and Processing
You hear a familiar song in the club or the restaurant. You listened to this song a thousand times long ago, and the sentimentality of the song really touches your heart. You desperately want to heart it tomorrow, but you can’t remember its name! Fortunately, in our amazing futuristic world, you have a phone with music recognition software installed, and you are saved.
But how does this really work? Shazam’s algorithm was revealed to world in 2003. In this article we’ll go over the fundamentals of that algorithm.

Jovan Jovanovic
Jovan is an entrepreneur and engineer with a strong mathematical background and an extensive skillset for problem-solving.
Microsoft HoloLens Review - Bridging The Gap Between AR And VR
Microsoft has a long tradition of spicing up relatively dull product announcements with compelling tech demos, and the Windows 10 announcement was no exception. The software giant used the opportunity to create a fair amount of buzz about the HoloLens, a futuristic headset that offers a glimpse into the future of Augmented Reality (AR).

Nermin Hajdarbegovic
As a veteran tech writer, Nermin helped create online publications covering everything from the semiconductor industry to cryptocurrency.
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MIDI Tutorial: Creating Browser-Based Audio Applications Controlled by MIDI Hardware
Modern web browsers provide a rich set of APIs; some of which have been around for a long time, and have since been used to build powerful web applications.
Web Audio API has been popular among HTML5 game developers, however, the Web MIDI API and its capabilities have yet to be utilized. In this article, Toptal engineer Stéphane P. Péricat guides you through the basics of the Web MIDI API, and shows you how to build a simple monosynth to play with your favorite MIDI device.

Stéphane P. Péricat
Stéphane is a front-end engineer with 7+ years’ of experience. He specializes in building performant JavaScript-based web applications.
Needle in a Haystack: A Nifty Large-scale Text Search Algorithm Tutorial
When coming across the term “text search,” one usually thinks of a large body of text which is indexed in a way that makes it possible to quickly look up one or more search terms when they are entered by a user. This is a classic problem in computer science to which many solutions exist.
But how about a reverse scenario? What if what’s available for indexing beforehand is a group of search phrases, and only at runtime is a large body of text presented for searching?

Ahmed Alamir
Ahmed is an Android expert with a passion for intuitive user experience and snappy app performance.
Making an HTML5 Canvas Based Game: A Tutorial Using AngularJS and CreateJS
There are many programming platforms used to develop games, and there are a plethora of devices to play them on, but when it comes to playing games in a web browser, Flash-based development still leads the way.
What if we could port these games to HTML5 Canvas technology and play them on mobile browsers as well? In this article, Toptal engineer Avinash Kaza gave a solution to this.

Avinash Kaza
Avinash is a senior developer with experience designing & developing data visualizations.
Video Game Physics Tutorial - Part I: An Introduction to Rigid Body Dynamics
Simulating physics in video games is very common, since most games are inspired by things we have in the real world. Rigid body dynamics – the movement and interaction of solid, inflexible objects – is by far the most popular kind of effect simulated in games.
In this series, rigid body simulation will be explored, starting with simple rigid body motion in this article, and then covering interactions among bodies through collisions and constraints in the following installments.

Nilson Souto
Nilson (dual BCS/BScTech) been an iOS dev and 2D/3D artist for 8+ years, focusing on physics and vehicle simulations, games, and graphics.
Advanced Java Class Tutorial: A Guide to Class Reloading
In Java development, a typical workflow involves restarting the server with every class change, and no one complains about it. But is Java class reloading that difficult to achieve? And could that problem be both challenging and exciting to solve? In this article, I will try to address the problem, help you gain all the benefits of on-the-fly class reloading, and boost your productivity immensely.

Lê Anh Quân
Lê has 14 years of experience building web apps, using Java technologies. Over the past 5 years, he has with React and Angular.
From the Ground Up: How I Built the Developer's Dream Keyboard
Going from a software background, knowing nothing about electronics, to designing and building a powerful, marketable hardware device is an interesting and fascinating experience. In this article, I’ll describe the design of how this electronic masterpiece works.

László Monda
László is a versatile full-stack developer experienced in a wide range of languages and frameworks with a system-wide understanding.
Blockchain Technology Explained: Powering Bitcoin
Bitcoin blockchain is the backbone of the network and provides a tamper-proof data structure, providing a shared public ledger open to all. This article provides insight in blockchain technology, current status and its potential.

Nermin Hajdarbegovic
As a veteran tech writer, Nermin helped create online publications covering everything from the semiconductor industry to cryptocurrency.
Context Aware Applications and Complex Event Processing Architecture
Since almost all smartphones today are equipped with location sensors, motion sensors, bluetooth, and wifi, today’s mobile apps can use context awareness to dramatically increase their capabilities and value. This article walks you through building a context aware app that employs complex event processing.

Rahul Devaskar
Rahul is a professional software engineer with leadership experience and expertise building full-stack React.js/Node.js applications.
A Tutorial for Reverse Engineering Your Software's Private API: Hacking Your Couch
Reverse engineering and hacking are usually related to malicious activities that result in sleepless nights of engineers responsible for system maintenance.
Reverse engineering is a tool that we can utilize to find the flaws and improve our software in many aspects. This article shows us how to use these techniques to learn more about different implementations of web API.

Nikolay Derkach
Nikolay (MSc) started his career with a Google internship, worked full-stack, built iOS apps, and now loves to help startups launch MVPs.
React.js View State Management Tutorial
One of the biggest and most common problems in front-end web development is state management. A developer is constantly focused on keeping the state object in sync with its view and the DOM representation. Users can interact with the application in many ways and it’s a big task to provide a clean transition from one view state to another.
We will see how using React JavaScript library can help us reduce application complexity and offload UI transitions from our application.

Leonardo Andrés Garcia Crespo
Leonardo is a life-long tech lover, he is always trying to learn something new while keeping up to date with favorite technologies.
The Publish-Subscribe Pattern on Rails: An Implementation Tutorial
The publish-subscribe pattern (or pub/sub, for short) is a messaging pattern where senders of messages (publishers), do not program the messages to be sent directly to specific receivers (subscribers). Instead, the programmer “publishes” messages (events), without any knowledge of any subscribers there may be.
This article provides insight in how to use the pub/sub pattern, in Rails, to communicate messages between different system components without these components knowing anything about each other’s identity.

Ahmed AbdelHalim
Ahmed is a back-end (API) developer who loves building useful and fun tools. He also has experience as a web developer.
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