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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.
from description:
"The string has a length greater or equal to one and contains only letters from a to z."
I think that it is not an issue.
shouldn't there be another filter saying ch < 'a' since you don't want character less than 'a'? Checkout your solution for input string "aaabbbmmmA"