1A2B (Bulls and Cows)

1A2B, also known as Bulls and Cows, is an exciting paper and pencil game.In the game, the android machine creates from 3 to 8 digits of random numbers. The digits must be all different. Then the player try to guess the secret number. If the matching digits are in their right positions, they are "a", if in different positions, they are "b".
For example, if theSecret number: 4271Your try: 1234Answer: 1a2b (The a is "2", and the b are "4" and "1".)