Minimum Adjacent Swaps for Ball Grouping

Question

A row of colored balls is written as a string balls, one character per ball: 'R' stands for a red ball and 'W' for a white one. A single move exchanges two balls that sit next to each other, and no other kind of move is allowed. Find the fewest moves needed so that every red ball ends up in one unbroken block. If the red balls already form such a block, the answer is 0. ...