Guess Number Battle

Guess Number Battle (also known as Bulls & Cows, 1A2B) is a simple puzzle game. The rule of the game is very simple. Firstly, the players choose 4 digits from 0 to 9. The digits must be all different. Then, in turn, two players try to guess the number who the opponent chose. The result will show "A" if the matching digits are on their right positions.