My understanding is that Array#include? iterates though until it finds a match; O(n).

Recall that [Sets are really just hashes](https://github.com/ruby/ruby/blob/trunk/lib/set.rb#L239) with objects as the key, and values of true. So Set#include? is just checking if the hash has that key; O(1).

Set#any? is implemented using #each, so it iterates over the hash keys; O(n).