Game to eleven

Problem

"To eleven, win by two," the umpire says before every ping-pong game at the club. The first player to reach 11 points wins, but only with a lead of 2 or more: at 10 all, play goes on until someone pulls ahead by 2. Write a function that takes the points in order, as a string where each letter is a point for player A or player B, and returns "A" or "B", whoever won. If the game isn't over yet, or the string is empty, return "". Eleven A in a row: A wins 11 to 0. At 11 to 10 there is no winner yet; at 12 to 10 there is.

As soon as someone wins, the game is over: if the string has more letters after that, ignore them.

Examples

• Eleven to nothing

  "AAAAAAAAAAA" → "A"

• B wins 11 to 5

  "ABABABABABBBBBBB" → "B"

• Not over yet

  "AABBA" → ""

• 11 to 10 is not enough

  "ABABABABABABABABABABA" → ""

• Long deuce, B wins 14 to 12

  "ABABABABABABABABABABABBABB" → "B"

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def winner(points):
    pass

function winner(points) {
}