输入一个四位数,共八次机会,A代表数字和位置均正确,B代表数字正确,但位置不正确.比如:A2B1代表三个数字正确,两个位置也正确-input a four-digit, a total of eight opportunities, A representative of the number and location are correct, B representative figure to be right, but not the correct position. For examp