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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.
Had the same problem. I figured out that it was due to having excess spaces between the answer. Used return str.trim(), and the error was gone.
Good Point. However, the specification states the function will only be passed two square matrices (N x N).