3 ms·

By never finding a cycle, it proves the graph is a DAG.

• jerf 2y ago
  But you have to run it on a sequence, or perhaps even more accurately, something that is putatively a sequence but may have an infinite loop in it. Tortoise & hare requires an unambiguous "next" function, which a graph does not have. Modifying it to not require that so it can run on a graph may be possible but that would constitute a different algorithm for sure, with different complexity analysis, etc.