Computational complexity theory books
Classic texts on computational complexity include Hopcroft &amp; Ullman's text {1} and Sipser's text {2}.  With patience, they should both be accessible.



{1} Hopcroft, John E., R. Motwani, and J. D. Ullman. "Introduction to Automata Thoery, Language, and Computation (2nd edition)". Addison-Wesley, Reading (2001).

{2} Sipser, Michael. Introduction to the Theory of Computation. Cengage Learning, 2012.