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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.
Did you evaluate the asymptotic complexity of the algorithm? It is probably O(n log(n)), where n is the number of digits of the number (you need n steps to find the first digit to swap, and then you want to sort the digits on the right). I guess hard numbers are hard only if the algorithm is wrong, but I see a lot of people whose program times out so I guess they already trip in bad cases...