Where Did All the Code Playgrounds Go?

I wanted to get better at technical interviews. That's really where this story starts.

A Course, Two Platforms, and a Problem

A couple of years ago I was taking Master the Coding Interview on Udemy — a course from ZTM (Zero to Mastery). It covers the fundamentals well: what algorithms actually are, what data structures do, and the relationship between time and memory that underlies almost every engineering decision you'll ever make. Many people criticize it. I thought it was good.

The instructor taught everything using Replit. All the examples, all the live coding — it happened right there in the browser. And Replit, at the time, was genuinely impressive. It felt like having a small VM at your fingertips. You could write code, run it, even get a terminal. Visually it was clean, comfortable to write in. I liked it.

But at the start of the course, the instructor mentioned something: if you want to follow along without paying for Replit, try Glot.io. So I did.