[rramadass]

Two books (get used copies for cheap);

* Foundations of Computer Science - http://infolab.stanford.edu/~ullman/focs.html

* Specifying Software: A Hands-On Introduction - https://www.amazon.com/Specifying-Software-Hands-Introductio... The name is a misnomer. See the ToC. This is actually a practical introduction to CS theory.

[davismwfl]

Pretty cool that the authors on the Foundations of Computer Science make the chapter PDF's available free since it is no longer in production. Just skimming through parts of it, definitely seems like a good learning resource.