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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.
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Fairly new to regex myself. I wondered the same after reading your comment and found this SE thread very informative.
http://programmers.stackexchange.com/questions/113237/when-you-should-not-use-regular-expressions
Thank you, this function really doesn't work in this case. However, there is the following statement
in the task: "reverse function should be executed only N times", so this case is impossibe, but thank you again, I changed my solution.