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

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.

valkum on May 2, 2021 [–]

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