A16337 · Secret Sport

题目描述

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.

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.

输入 #1

7
5
ABBAA
3
BBB
7
BBAAABA
20
AAAAAAAABBBAABBBBBAB
1
A
13
AAAABABBABBAB
7
BBBAAAA

输出 #1

A
B
A
B
A
B
A