Secret Sport
Let's consider a game in which two players, A and B, participate. This game is characterized by two positive integers, $$$X$$$ and $$$Y$$$.The game consists of sets, and each set consists of plays. In each play, exactly one of the players, either A or B, wins. A set ends exactly when one of the players reaches $$$X$$$ wins in the plays of that set. This player is declared the winner of the set. The players play sets until one of them reaches $$$Y$$$ wins in the sets. After that, the game ends, and this player is declared the winner of the entire game.You have just watched a game but didn't notice who was declared the winner. You remember that during the game, $$$n$$$ plays were played, and you know which player won each play. However, you do not know the values of $$$X$$$ and $$$Y$$$. Based on the available information, determine who won the entire game — A or B. If there is not enough information to determine the winner, you should also report it.
In the first test case, the game could have been played with parameters $$$X = 3$$$, $$$Y = 1$$$. The game consisted of $$$1$$$ set, in which player A won, as they won the first $$$3$$$ plays. In this scenario, player A is the winner. The game could also have been played with parameters $$$X = 1$$$, $$$Y = 3$$$. It can be shown that there are no such $$$X$$$ and $$$Y$$$ values for which player B would be the winner.In the second test case, player B won all the plays. It can be easily shown that in this case, player B is guaranteed to be the winner of the game.In the fourth test case, the game could have been played with parameters $$$X = 3$$$, $$$Y = 3$$$: In the first set, $$$3$$$ plays were played: AAA. Player A is declared the winner of the set. In the second set, $$$3$$$ plays were played: AAA. Player A is declared the winner of the set. In the third set, $$$5$$$ plays were played: AABBB. Player B is declared the winner of the set. In the fourth set, $$$5$$$ plays were played: AABBB. Player B is declared the winner of the set. In the fifth set, $$$4$$$ plays were played: BBAB. Player B is declared the winner of the set.In total, player B was the first player to win $$$3$$$ sets. They are declared the winner of the game.
Each test contains multiple test cases. The first line contains a single integer $$$t$$$ $$$(1 \leq t \leq 10^4)$$$ - the number of test cases. The description of the test cases follows.The first line of each test case contains an integer $$$n$$$ $$$(1 \leq n \leq 20)$$$ - the number of plays played during the game.The second line of each test case contains a string $$$s$$$ of length $$$n$$$, consisting of characters $$$\texttt{A}$$$ and $$$\texttt{B}$$$. If $$$s_i = \texttt{A}$$$, it means that player A won the $$$i$$$-th play. If $$$s_i = \texttt{B}$$$, it means that player B won the $$$i$$$-th play.It is guaranteed that the given sequence of plays corresponds to at least one valid game scenario, for some values of $$$X$$$ and $$$Y$$$.
For each test case, output: $$$\texttt{A}$$$ — if player A is guaranteed to be the winner of the game. $$$\texttt{B}$$$ — if player B is guaranteed to be the winner of the game. $$$\texttt{?}$$$ — if it is impossible to determine the winner of the game.
for jsgenskj in [*open(0)][2::2]:
    print(jsgenskj[-2])
for s in [*open(0)][2::2]:
    print(s[-2])
for s in [*open(0)][2::2]:
    print(s[-2])