Bulls and Cows Game

How to play:

Bulls & Cows is a logical puzzle game in which you have to guess a secret four digit code selected by the android.
All four digits of this secret code are different. Each digit can be any number from 0 to 9.
You can start with a random four digit code as a guess by using the on-screen keyboard.
If a digit from your guess matches but is not in the correct position in the secret code, its a 'Cow'.
If a digit matches and it is in the correct position, its a 'Bull'.
The goal is to get four bulls in the least guesses!

Example:
Secret code - 4596
Guess - 5193
Result - 1 Bull and 1 Cow (5 is a cow and 9 is a bull).