Level 6. Expert Topics
Flows, suffix structures, and computational geometry — international-level topics.
International-level topics: flows, suffix structures, computational geometry. Here the lessons are gateways into each topic, not complete courses: whole books exist on every one. Take them on when you are confident with levels 1–5.
Beyond that — only practice: contest archives, editorials of strong solutions and regular competitions. Come back to the lessons as a reference — and good luck at the olympiads!