Bulls and cows

Classic code breaking game where you must guess a 4 digits number.

In this game you must guess a 4 digits number, where each digit appears only once.
Each guess you make, it will be displayed the number of digits which are in the right place 'Bulls' represented by the letter B, and the number of digits which are in the number but in another position.

The game 'Mastermind' was inspired by the original version of this game.