I have a question regarding Div 3/4 editorials: Why isn't range trees being used in any problem except last Div 3 problem? Many problems seems more intuitive to do with range trees than with sets. No need for iterators and is certainly more flexible, too. One such example I have seen is 1374E2 - Чтение книг (сложная версия), where two Fenwick trees with binary lifting is, in my opinion, more direct and easy to understand than the editorial's solution.