147. Pick up stones

easy  - accepted / - tried

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.

// 'B'

// 'A'

// 'A'

// 'B'

Bugfree ordinary solution is better than buggy fancy ones.