It sets the 'case-insensitive' flag for the remaining pattern

what's (?i) for?

How is this library not banned on codewars?!

I really liked this one, but I think the description could use a little more "redundancy". I mean it's precise (i.e. it describes the problem completely) but I had a hard time figuring out some details. Just a little explained example, e.g. for testDownAndDown or testTrickyQueues could really help. However, analyzing the test cases and figuring this out was kind of an interesting part too, so ...

/** @exception NullPointerException if <code>input</code> is null. */

One thing is missing. Null input check.

I added what was neccessary.

@JustyFY But in Java, you put a List as the parameter, so it's neccessary to import List, isn't it?

You're (hehe) actually right about this one, but I think this concerns almost all other solutions as well, since it was not specified in the kata description that contractions should be respected. Also, regarding the kata rank, I suppose that it was not intended either. Translating "you're" to "your sister is" would require a much more complex regex/algorithm.

I think you're will error handling into your sister're

"Hello sorry for the late replay but usually setup doesn't include all the tools needed to complete the exercise."

BS! Your setup doesn't even include the tools to set it up!

Very sophisticated solution! I was not aware of "\b" yet, so I definitely learned something new. thx!

Hello sorry for the late replay but usually setup doesn't include all the tools needed to complete the exercise.
Differnet people might use diffrent ways so I wouldn't add that in if you agree. It narrows creativity. Next time it is better to mark it as suggestion thank you in advance.

I agree, totally frustrating ... I've spent way more time on the unicode thing than on the algorithm, because this was the first time I've encountered unicode in python.