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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.
Hi, as the "chars" string is sorted, you don't have to use Contains which will scan the all string. You can compare to the last character of result to determine if addition of character is ok.
Look at my solution.
strings.Builder is apparently more efficient to concatenate strings. https://golang.org/pkg/strings/#Builder