bbbbbbb

1. 最左边B向左移动7次:ABAAAAAAABBBBBBB

2.后面最左边的B向左移动6次:ABABAAAAAABBBBBB

3.后面最左边的B向左移动5次:ABABABAAAAABBBBB

4.后面最左边的B向左移动4次:ABABABABAAAABBBB

5.后面最左边的B向左移动3次:ABABABABABAAABBB

6.后面最左边的B向左移动2次:ABABABABABABAABB

7.后面最左边的B向左移动1次:ABABABABABABABAB