get yourself a discrete math textbook (I can't remember what I used). A sprinkling of things that will come up: set theory, probability (Bayesian), Big-O notation and associated meanings, worst/best/avg case analysis, amortized cost, induction, some algebra, ect

if you don't really understand all the math surrounding some fancy algorithm it probably isn't all that important. and everyone's favorite line in a CS proof is of course "without loss of generality".