Loading collection data...
Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
This comment is hidden because it contains spoiler information about the solution
I like this one. So you check to see whether the index of is equal to the last index of, which is a shortcut to see whether there is more than one instance of that letter.
It's also cool that you can achieve basically the entire goal in 2 lines because string.replace takes a callback. Sweet :)
Nice one :) Didn't think to use a RegEx for this - reminded me not to treat map like a hammer!