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In a (much) earlier post of mine, I discussed a puzzle called Top Spin (once made by Binary Arts), in which 20 beads were placed on an oval track with a turntable that could flip the four beads that occupy it. I showed that it was possible to reverse the order of the beads, from [1, 2, 3, ..., 19, 20] to [20, 19, ..., 2, 1], even if the beads were placed on a straight track instead of an oval one.

In my previous post, I shared some of my thoughts on the CodeCrafters website and the coding challenges it offers. In particular, I had completed the HTTP server challenge in Rust and Claude Code challenge beta (notably, the number of available stages, and the feature set of the “completed” code, are quite limited) in Python and was working on the Interpreter challenge in Rust. I have since completed the Interpreter challenge, and decided to share some more thoughts on the experience.

CodeCrafters is a site where one can complete a number of programming challenges. Challenges include: Build your own HTTP server Build your own Interpreter Build your own Shell Build your own Claude Code (still in beta) Each challenge is broken into a number of steps, with an extensive test suite triggered by the command codecrafters submit which: Pushes your submission to a Git repo on the CodeCrafters server Runs the tests for the given step Reports results back to the user in the terminal Supposedly, this is made possible by Git’s post-receive hook, which runs the test suite and reports the results back to the user via Git’s side-channel communication capabilities (as well as updating the user status in Codecrafter’s database if the step was cleared sucessfully).

Top Spin was a puzzle in which 20 beads were placed on an oval track with a turntable, such that any four consecutive beads could be flipped. Naturally, I wondered whether it was possible to reverse the order of the beads, from [0, 1, ..., 19] to [19, 18, ..., 0]. As it turns out, this is possible even if the beads are placed on a straight track instead of an oval one.

This post refers to a previous version of my personal website, which was built using MkDocs. The current version of my website is built using Hugo, and the content of this post may not be relevant to the current version. A referenced Python package below, mkdocs-bibtex, is no longer maintained. In my new Hugo-based website, this package is not necessary — the Taho theme for Hugo providing a built-in solution for displaying publications from a YAML file, which is generated using pybtex directly (mkdocs-bibtex used pybtex as a dependency).