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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.
You don't need the nodes' values. They might not even have values.
Yes, 421 people have did it in fact. Your code is wrong and not optimized. Doing semi-based recursion is not the way to solve this. You may resort to character-by-character analysis and find some properties of multiplication.