It is widely known; just Google it. In my case, I didn't expect to get hired, but I received an offer. Overall, it was an exhausting but interesting experience. It reminded me a bit of university, like an exam. I enjoyed myself a lot because I wasn't nervous. If you are nervous, I agree it can be a nightmare.

Lots of algorithms, from low abstraction level to high level.

I was lucky to know some of the answers or be on the right path for them.

Some problems are just impossible, literally. They just want to see how you think and behave.