Tortoise and hare agorithm is an interesting one to look up. You’ll never use it in practice, but it’s clever.

Anecdatum, but I've used it on an embedded target to check that datastructures loaded from flash didn't get corrupted.

When reading the story, I thought, "well of course that's the solution ...", but then couldn't recall ever learning it. I'm grateful that someone shared the name, as Wikipedia's explanation is surprisingly clear:

https://en.wikipedia.org/wiki/Cycle_detection#Floyd's_Tortoi...

Hopefully by the end of today you can know something about all of them!