I'm a freshman CS major and find both of these topics really interesting, but I also find them difficult (I've been told this isn't much of a surprise!).
I was hoping some of you could direct me towards some sources to supplement what I'm learning. I visited a few relevant questions posted before, but the one good one that had sources provided links that are now broken!
Thanks!
You will probably want to start off with a Discrete Math textbook, which will introduce you to relevant mathematical preliminaries as a CS major. Certain combinatorial arguments rely on your understanding of functions and basic set theory, plus it helps formalize intuition. So this is really a good starting point. Epp's Discrete Math text is pretty friendly and has a good covering of set theory, functions, relations, basic combinatorics, and graph theory (which is closely tied to combinatorics).
I'd avoid Alan Tucker's Applied Combinatorics text. It is a good book for problems, but not much else.
Nick Loehr's Bijective Combinatorics text is quite good, but is geared towards advanced undergrads and grad students. It might be a good text for later.
A personal note: I found combinatorics quite perplexing the first time I saw it, which was when I was a senior in high school. I had a good teacher, but didn't get it. I liked it more when I took a class in college, and I've continued to develop an intuition for it. It is quite a difficult subject and requires a lot of intuition. However, it is very rewarding in training your brain and helping in other subjects (such as linear algebra, where you can really utilize bijective counting arguments in your linear transformations unit). Don't get too frustrated if you struggle with it the first time around.
Best of luck! :-)