I'd say probability theory and combinatorics, graph theory, algorithms, and computational geometry are most relevant to roguelikes. Although it's not exactly a book about algorithms, SICP is worth reading. Graph theory is sort of a deceptive phrase because it's not like there's a single canonical body of knowledge to look at -- it's extremely diverse and any introductory text primarily reflects the interests of the author rather than what are really the most important things to know for any particular purpose. You at least want to have the basic vocabulary -- graphs, trees, paths, cycles, planarity, multiple connectedness etc. Certain algorithms in graph theory are worth knowing about, e.g. min/max spanning trees, Dijkstra, A-star. Some probabilistic graph theory can provide useful intuition relevant to map generation.

I don't know any good introductory books on probability or combinatorics that are aimed at a general audience. You could probably just go to a used book store near a university campus and pick up something that's used for an introductory course in probability. You can probably find something relatively old and cheap that will serve your purposes.