def check(secret, guess):
    secret = list(secret)
    guess = list(guess)

    cows = 0
    for i in range(len(secret)):
        if secret[i] == guess[i]:
            cows += 1
            guess[i] = None
            secret[i] = None
    bulls = 0
    for i in range(len(secret)):
        if secret[i] is None:
            continue
        for j in range(len(guess)):
            if secret[i] is not None and guess[j] is not None and secret[i] == guess[j]:
                guess[j] = None
                bulls += 1
                break
    return f'{cows}A{bulls}B'

print(check("1807", "7810")) # "1A3B"
print(check("1123", "0111")) # "1A1B"