I run a (paid) newsletter that sends fun coding interview puzzles every day. If you're interviewing around (or if you just enjoy programming problems), check out Daily Coding Problem: https://dailycodingproblem.com/!
I'm obviously biased but I think the problems are fun and the solutions are valuable. Here are some blog posts I wrote that hopefully give you an idea of our questions:
Given a table of currency exchange rates, determine whether there is a possible arbitrage: https://dailycodingproblem.com/blog/2018/01/02/find-an-arbit...
Picking a random element from an infinite stream: https://dailycodingproblem.com/blog/2017/11/30/random-elemen...
Merging k sorted lists: https://dailycodingproblem.com/blog/2017/11/29/how-to-solve-...