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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.
Well, those numbers appear only 1 time. And you wanted to list all numbers that appear an odd number of times, so, it works as expected.
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Don't worry, discuss solutions in Solutions next time, and even there, mark your post as having spoiler content when needed, otherwise your posts there are also shown in the home page.
About your question, if you only need to return the single number that appears an odd number of times, why do you need the other function?
Please don't post solutions in Discourse.