One of the easiest ways (for me) to spot AI code on a homework assignment has been to ask myself a simple question. Is this code something that would make sense for a human to write. It doesn't catch all cases - it doesn't catch even the majority of cases - but it does filter out people who just took the assignment and pasted it in to a prompt.

Mirroring the example provided in the article I once saw a 200 line class implementation for tridiagonal matrices in python - where a simple numpy command would suffice and perform an order of magnitude better.