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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.
who said you didn't have to "search"? ;) But there are some case that are clearly invalid too (input validation), so no need to "search" for those.
I'm not sure I understand the assignment here. How am I supposed to figure out if a puzzle is unsolvable without searching.. literally every sudoku board that could generate from the seed I'm given?