One of them was a compilers course done by karpathy. It was pure joy and a great learning experience.
Also in my experience the joy of doing a course was much stronger correlated with the teacher's qualities rather than the subject itself.
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however I could dig out the references to it. Apparently it was a course by Prof. Alex Aiken and karpathy was a TA.
This repository seems to be a future version of the same course. https://github.com/gboduljak/stanford-compilers-coursework
Edit: found the videos from the course on the archive https://archive.org/details/academictorrents_e31e54905c7b266...
