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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.
Wow, & is a good use
Thanks for the pointer (no pun intended)! In hindsight that's a clear optimisation.
I think this is O(n^2) because String.sub creates a new string on each call.
I had the same idea. I avoid creating a new string by keeping track of two pointers, beginning and end.