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If you're just looking for the algorithms, there's always this C# port (from 7 years ago): https://github.com/angellaa/algs4

Interestingly, the README includes an e-mail exchange with Kevin, who noted the code is GPL

It looks like the original code is located here: https://algs4.cs.princeton.edu/code/

Found this in the link you provided. As you can see from the code there is a GPL license footer on each file.

This site even links to the now taken down Git repo.