Hey there, I am new on codeforces and I wanna train, therefore I might represent my country in the upcoming ACM or even ICPC. I felt like there is a gap between the B and C problems difficulty, most contests I viewed, problems numbered A ,B were very easy, however problems C, D, & so on were very difficult. I may think that this is the point I cannot pass , because I want to train on medium difficulty problems , what do you suggest? codeforces!
UPD1 I have improved a lot since last year! It was accomplished by studying many algorithms such as in Graph(dfs, bfs, dijkstra, topological sort) and in divide and conquer such as (dynamic programming, binary search) and data structure ( segment tree, trie, prim, BIT..). you can search Youtube for good tutorials for these algorithms/data structures. even though problems div1D div1E... still are very difficult.