Andur's Game Solutions

Includes warmup problems minus anagrams, (very poorly written) Tower of Hanoi, and Mastermind with trivial AI (the game intentionally does not specify which slots are correct, only how many).
for constants like these, I would actually have defined them implicitly

def top_border
'–'
end

doing that saves a little bit of memory and speed, actually, as well as making it more clear that these elements are meant not to change mid-execution. I guess you also could have defined them as constants, but if I recall, Ruby constants are usually worth shying away from.