Topological Sort
Order tasks so every prerequisite comes first — and detect when no such order exists.
This topic is part of Pro.
Free covers the C and Python courses, the first three DSA topics, the opening system design lessons and the beginner AI lessons, all with the full coach. Pro opens the rest of the library in the FollowtheDamnCode app.
What is in it
- 1Ordering dependenciesModel "a before b" as a directed edge; a valid order exists exactly when there's no cycle. Pro
- 2Kahn's algorithm (BFS)Repeatedly take a vertex with no remaining prerequisites; if some are never freed, there's a cycle. Pro
- 3Topological sort with DFSA vertex finishes only after everything it points to — so reverse finish order is a valid order. Pro