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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.
I don't think that the idea of the problem solving is to utilize built-in function in php
The description says strings not words, so spaces should be allowed. All solutions based on implode are invalid and passing just because there is a missing test case.
wouldn't work if "words" were allowed to have spaces inside.