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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.
I have got the same problem.
Additionaly I got case with number '7' repeated 8th times, that was the content of vector, the test said that expected number is: 0, but I believe that description of the task is clear: "There will always be only one integer that appears an odd number of times.", so this is another bug.