Hello all today I struggled a lot with C2, especially because I am not used to using sets, actually not used to using any data structure other than map or vector, I have used queues for BFS only. So I have decided to spend a few days with them.

Please suggest some problems, which are not higher than maybe 2000 rated on CF equivalent, which cannot be solved in desired time or memory without specific data steuctures. One example is stacks for finding the nearest element smaller in the left/right using stack (or vector with push back). Another example maybe using sets to maintain indexes of appearances with updates, which was used in C2. Some people say some sorts of balanced paranthesis substring problems can be solved only using stack but I have only ever used a map for that purpose at best.