LOL to those who voted 'Best Practices'. This is NOT a best practice. I used it because I didn't think about the safer fetch which is superior.

Kinda threw that rescue in there, had one case failing LOL

Convoluted, but I like it :)

This is my favorite answer. Everything is simplified as much as possible without sacrificing the readability of the variable names. Well done.

This solution seems to assume you can't refactor the Node class.

Beautiful!

This method was created for this kata. Probably the only time it's ever been used LOL

No, I did that and it passed all tests. I'm a bit disappointed that there wasn't a test that invalidated the answers which didn't add your points.

This one's my favorite. Very concise and readable. Nice

I think you wanted

(0..9).include? a

If you're going to check length, you may as well do it with the built-in length checking in Regex :).

Also, avoid return true / else return false structures. You can use pin.match? which will return that for you.