Think of courses as nodes and prerequisites as directed edges. If there's a cycle, you can never complete all courses. The question becomes: detect if a directed graph has a cycle. Use DFS with three states: unvisited, visiting (currently in DFS path), visited (fully explored). If you reach a "visiting" node, you've found a cycle.
##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
$ curl repovive.com/roadmaps/maang-interview-prep/graphs/course-schedule-hint
░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░█████████████████████████████████████████████████████████████████████████████