Can you recommend me a book or (better!) a site with many hard problems and exercises about data structures?

I'm already answering project Euler questions, but these questions are about interesting, but uncommon algorithms. I hardly used even a simple tree. Maybe there is a site with exercises like: hey, you need to calculate this: ... . Do it using a tree. Now do it using a zipper. Upload your C (Haskell, Lisp, even Pascal or Fortress go) solution. Oh, your solution is so slow!

Self-education is very hard then you trying to learn very common, fundamental things. How can I help myself with them without attending to courses or whatever?