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 is a great demonstration of how terrible is codewars ranking system.
At least add buttons "Bad Practices" and "Bad Complexity".
What is currently here teaches people bad things and reinforces wrong opinions about code.
The very first problem and such a poor quality, ouch. I bet a lot of people got frustrated by this. The problem should explicitly specify that each element of the first array can only be used once. It is a critical information to pass the testcases and it's only natural to assume that you can view input arrays as sets (unless EXPLICITLY specified otherwise).