147. Pick up stones

There is a pile of n (n > 0) stones.

Player A and Player B take turns to pick 1 or 2 stones from the pile. A starts first.

Who picks the last stone loses the game.

Now here is the question, is there a winning strategy for A or B ? If so, returns the player name. If there is none, return null.

winningStonePicking(1)// 'B'winningStonePicking(2)// 'A'winningStonePicking(3)// 'A'winningStonePicking(4)// 'B'