> A place where, without the cludge of libraries, you could dive into a topic on data structures, apply search refinement until you find a structure that seems like the best match for what you want, and then implement.

Or, in my experience, a place where you can dive into a topic on data structures, apply search refinement until you find a structure with promising properties, be faced with an opaque wall of math, then copy/paste the data structure's name into Google and spend a day or two trying to find someone or something who will actually explain how to implement it in terms of bits and bytes, rather than polynomials over a Galois field.