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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.
On the ruby tests at least, it calls 'permsol' where the actual tests and the code want "permute'. It might be nice if these were consistent.
Not sure about other languages, but in ruby, the "Not a string" and "Not letters" return values, should probably throw an ArgumentError. Also, it wasn't obvious what was supposed to happen with blanks at the beginning and end of the phrase. You might want to mention that they should be stripped off (or at least that's what it took for me to get it to work).
Same thing here ... I added this test case
Test.assert_equals(prefill(0,1), [])
and it suceeds locally. This is with ruby. Any thoughts?