Methods for quick learning?

Question

Discrete Math

The question is rather banal, on Wednesday there is an exam in programming, on Saturday in math. With programming, everything is fine, but in general, almost no time has been invested in mathematics. The last time I saw her at all was about 2 years ago (math. analysis).
So, maybe someone can advise how you can meet the deadlines well? For discrete mathematics, like programming, is learned by training, and to decide everything and look for someone else to check - I think there is not much time.
I think many here have gone through this, so I'm glad for any advice :) Maybe there are good sites for preparation? Or short and understandable books with examples and solutions to them.