Ask HN: where to find coding problems for pre-interview practice?

I'm going to be taking part in a week-long group interview with a major tech company soon. I'm excited and nervous, obviously. The focus will be on general coding ability. From the preliminary tests, I feel like I know this stuff but I'm rusty; I've been out of work for a bit, and while I'm familiar with all the core concepts, it sometimes takes me a bit of research to recall specific details--not a good place to be in a whiteboard situation. So, I want to brush up beforehand.

My contact recommended "reviewing basic data structures and practicing some coding problems you haven’t seen before." That's good, but vague. Any suggestions on where to find stuff like that? Google results have been pretty scattershot, with a lot of dubious paid review services. I'm willing to pay a bit, but I don't have much right now and I want to know I'm getting my money's worth.

Thanks! If you have any suggestions on better places to post this, I'd be happy to hear them.

Relatedly, I feel like I'm really good at analyzing data (taking a big set of data, which may be inconsistent and/or contain errors, and finding patterns in it), but I know nothing about "data analysis" as a professional field. Any suggestions on how to learn more about that, and (perhaps) bring it up in the interviews?