Ask HN: Most creative algorithms?

I recently stumbled upon Sleep Sort[1, 2], which is the most creative algorithmic idea I think I have ever seen in code.

I'd love to read about more creative algorithms and code snippets like this, what else is out there? And I don't mean obfuscated code (although they often do include very creative ideas too).

[1] https://rosettacode.org/wiki/Sorting_algorithms/Sleep_sort

[2] https://news.ycombinator.com/item?id=2657277

I'm partial to

https://en.wikipedia.org/wiki/Disjoint-set_data_structure

It's a fairly simple algorithm to implement, but there is some wicked-cool analysis behind how fast it is.

It's a super good thing to have in your toolbox for any time you want to do any sort of "simultaneous flood-fill everywhere" or "partition everything" task.