So I need to find the number of strings with 3 times 'A', 4 times 'Y' and 5 times 'Z' such that there are no consecutive same characters.
I was thinking from all strings to substract those with "AA", "BB" or "CC" as substring. But I can't find those. And to substract them maybe I need to use the inclusion-exclusion principle, but I am not sure.
Any tips?
