1A2B also known as (Bulls and Cows) A classic game of guessing the opponent's secret number (4-Digits).
The challenge is to find the opponent's secret number with a minimum number of suggestions.

you can play against the mobile, or against a friend.

The players each write a 4-digit secret number. The digits must be all different. Then, in turn, the players try to guess their opponent's number who gives the number of matches. If the matching digits are in their right positions, they are "As", if in different positions, they are "Bs". Example:

Secret number: 4271
Opponent's try: 1234
Answer: 1 A and 2 B, (The A is "2", the B are "4" and "1".)
The first one to reveal the other's secret number in the fewest guesses wins the game.