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Guess number game: pick 4 digits from 0-9. one digit cannot pick twice.
Then, create a method to guess that number. If the position is right, marks "A". otherwise, marks "B". Then, count As and Bs.

For example, the answer is "1234", but guess "1024". Then the result is "2A1B".

With best guessing method (you need to find), and in worst situation, choose the maximum times the method needs to guess any 4 digits-non-repeat numbers.

Worst case : So, if the answer is cheated, it should do:
Choose the result that ends up with largest availablilities.

For example, it always replies first guess with "1B" (5040 -> 1440).

So, the second guess as a optimize guess method should pick the inside range one to gest smallest narrow down-ed range. So, the output looks like, for example:
1234 -> 1B
4096 -> 1B