As for me rank of this kata should 5 or even 6, too easy even with two for.

I'm the 4th who's solved this kata using Dart. It would be nice to include this point in description:

• awaited short link path should contain from 1 to 4 lower case letters, or just add regex [a-z]{1,4} into 'URL Shortener' section.

Thanks for this fun!

Completely dynamic solution, which will work with different rows, pins & field size counts.
Included calculation of side spacer size and element spacing condition.