I struggle to even understand those problems, I checked a lot of 1000-1200 graphs tasks, and I just don't understand them. https://mirror.codeforces.com/problemset/problem/2078/B
and the solution for that issue it is not understable for me.
https://mirror.codeforces.com/problemset/problem/217/A
A lot of the times, I read the problem, I don't understand fully the problem, the only problem I solved in that range is this one. not sure why it is 1100 https://mirror.codeforces.com/contest/1829/problem/E
I can say you that before 1500 there are no any graph tasks (maybe dfs on 1300-1400 rarely). If you see tag "graphs" at 800-1200 it's doesn't mean that you need to observe it as graph. In 99% cases this is math problem or constructive.
thank you for help
It's maybe foolish to say, but I recommend you to not learn topics that you don't need right now. There are a lot newbies that know segment tree, dsu, fft, but still haven't reached pupil. Because their brain full of disturbing things that they don't need
How about... matrix multiplication?
If you consider it in the context of linear algebra, then it is always useful and interesting. But if you are talking about the k matrix multiplication algorithm, then this is a dp topic for 2400+