Hello! I have been coding in c++ for a year. I am studying A-level and I want to prepare for IOI. But I realised that i have to take part in NOI(national olympiad of informatics). So, how to prepare for regional and national level?

Would love to hear the experiences of people who went to IOI.

Can I write Zco first or should I follow the order

which language is better and easy to learn ?

INOI is coming up soon, and seeing that only C++98 was provided in ZCO, I won't be surprised (but would be upset) that they provide the same in INOI.

Normally I represent undirected graphs as an unordered_map of vectors, like this:

unordered_map <int, vector <int>> graph;

For directed graphs, I may use an unordered_map of unordered_maps to store the weights.

However, what is the best way to do so in C++98, especially for sparse graphs. Do I have to resort to something like: int graph[n][n] which would consume quite a lot of space, as it is basically just an adjacency matrix.

please suggest me some tips , Ideas aswellas strategy to conquer IOI.