2.後面最左邊的B向左移動6次:ABABAAAAAABBBBBB
3.後面最左邊的B向左移動5次:ABABABAAAAABBBBB
4.後面最左邊的B向左移動4次:ABABABABAAAABBBB
5.後面最左邊的B向左移動3次:ABABABABABAAABBB
6.後面最左邊的B向左移動2次:ABABABABABABAABB
7.後面最左邊的B向左移動1次:ABABABABABABABAB