Part a is pretty easy, I'm mainly concerned about part b which I have no idea how to approach. Thanks!

2. Alternating glasses a. There are 2n glasses standing next to each other in a row, the first n of them filled with a soda drink and the remaining n glasses empty. Make the glasses alternate in a filled-empty-filled-empty pattern in the minimum number of glass moves. [Gar78 b. Solve the same problem if 2n glasses-n with a drink and n empty-are initially in a random order