I'm teaching a data structures class w/java this coming fall semester, and am putting together a reference text/notes in markdown to provide for free, since it seems really silly to require a paid text for this stuff.

Every single item that contributes to the learning objectives of this course is incredibly Google-able, but as new students to the field, they do need at least some curation and direction to keep from getting overwhelmed. They need a reference resource that they can trust which is academic enough to be true, yet reasonably conversational. Textbooks used to fill this role, but publishers priced and walled-gardened themselves out of relevance.

Side note: if you're an professor who has done something like this in the past, I'd love to compare notes with you.