A simple logic game where you guess a generated number based on previous attempts.
The game tells you how close you are from the number.
A bull means your guess contains a correct digit in the right place, a cow means your guess contains a correct digit in the wrong place.
For example, if the guessed number is 6138, the output for guess 1234 shall be 1 bull, 1 cow, as the guess contains a 1 in the wrong place and a 3 in the right one.