the Link was updated to https://blog.ostermiller.org/finding-a-loop-in-a-singly-linked-list/

pretty slick way of forcing a string!

This script has a good balance of speed and its clean to read. Nice work.

My mind was blown away with "Catch Loops in Two Passes" approach! How elegant.

Great article, yep, I did use the last one. Since there is a tail before the loop, I need to call the method twice.

You have forgotten that one can use recursion!

Returning nil from a method which clearly should return either false or true can lead to bugs. E.g. alphanumeric?(s) == false wouldn't work as expected.

Cheats ;D

Nice and a different solution!

But everything other than nil and false are truthy in Ruby. There's no need to do an explicit boolean conversion.

Nice one regexp solution!

True coffeescript solution!

Nice solution.