CF1791C.Prepend and Append

Timur initially had a binary string$^{\dagger}$ $s$ (possibly of length $0$). He performed the following operation several (possibly zero) times:

• Add $\texttt{0}$ to one end of the string and $\texttt{1}$ to the other end of the string. For example, starting from the string $\texttt{1011}$, you can obtain either $\color{red}{\texttt{0}}\texttt{1011}\color{red}{\texttt{1}}$ or $\color{red}{\texttt{1}}\texttt{1011}\color{red}{\texttt{0}}$.

You are given Timur's final string. What is the length of the shortest possible string he could have started with?

$^{\dagger}$ A binary string is a string (possibly the empty string) whose characters are either $\texttt{0}$ or $\texttt{1}$.

蒂穆尔最初有一个二进制字符串$^{\dagger}$ $s$（长度可能为 $0$）。他执行了以下操作若干次（可能为零次）：

• 在字符串的一端添加字符 $\texttt{0}$，在另一端添加字符 $\texttt{1}$。例如，从字符串 $\texttt{1011}$ 出发，可得到 $\color{red}{\texttt{0}}\texttt{1011}\color{red}{\texttt{1}}$ 或 $\color{red}{\texttt{1}}\texttt{1011}\color{red}{\texttt{0}}$。

现给出蒂穆尔最终得到的字符串。请问：他最初可能拥有的最短字符串长度是多少？

$^{\dagger}$ 二进制字符串是指一个字符串（可能为空），其每个字符均为 $\texttt{0}$ 或 $\texttt{1}$。

The first line of the input contains an integer $t$ ($1 \leq t \leq 100$) — the number of testcases.

The first line of each test case contains an integer $n$ ($1 \leq n \leq 2000$) — the length of Timur's final string.

The second line of each test case contains a string $s$ of length $n$ consisting of characters $\texttt{0}$ or $\texttt{1}$, denoting the final string.

输入的第一行包含一个整数 $t$（$1 \leq t \leq 100$）—— 表示测试用例的数量。

每个测试用例的第一行包含一个整数 $n$（$1 \leq n \leq 2000$）—— 表示 Timur 最终字符串的长度。

每个测试用例的第二行包含一个长度为 $n$ 的字符串 $s$，由字符 $\texttt{0}$ 或 $\texttt{1}$ 组成，表示最终字符串。

For each test case, output a single nonnegative integer — the shortest possible length of Timur's original string. Note that Timur's original string could have been empty, in which case you should output $0$.

对于每个测试用例，输出一个非负整数——Timur 原始字符串的最短可能长度。注意，Timur 的原始字符串可以为空，此时应输出 $0$。

In the first test case, the shortest possible string Timur started with is $\texttt{0}$, and he performed the following operation: $\texttt{0} \to \color{red}{\texttt{1}}\texttt{0}\color{red}{\texttt{0}}$.

In the second test case, the shortest possible string Timur started with is $\texttt{11}$, and he performed the following operation: $\texttt{11} \to \color{red}{\texttt{0}}\texttt{11}\color{red}{\texttt{1}}$.

In the third test case, the shortest possible string Timur started with is $\texttt{10101}$, and he didn't perform any operations.

In the fourth test case, the shortest possible string Timur started with is the empty string (which we denote by $\varepsilon$), and he performed the following operations: $\varepsilon \to \color{red}{\texttt{1}}\texttt{}\color{red}{\texttt{0}} \to \color{red}{\texttt{0}}\texttt{10}\color{red}{\texttt{1}} \to \color{red}{\texttt{1}}\texttt{0101}\color{red}{\texttt{0}}$.

In the fifth test case, the shortest possible string Timur started with is $\texttt{101}$, and he performed the following operations: $\texttt{101} \to \color{red}{\texttt{0}}\texttt{101}\color{red}{\texttt{1}} \to \color{red}{\texttt{1}}\texttt{01011}\color{red}{\texttt{0}}$.

在第一个测试用例中，Timur 起始的最短可能字符串是 $\texttt{0}$，他执行了如下操作：$\texttt{0} \to \color{red}{\texttt{1}}\texttt{0}\color{red}{\texttt{0}}$。

在第二个测试用例中，Timur 起始的最短可能字符串是 $\texttt{11}$，他执行了如下操作：$\texttt{11} \to \color{red}{\texttt{0}}\texttt{11}\color{red}{\texttt{1}}$。

在第三个测试用例中，Timur 起始的最短可能字符串是 $\texttt{10101}$，他未执行任何操作。

在第四个测试用例中，Timur 起始的最短可能字符串是空字符串（我们记为 $\varepsilon$），他执行了如下操作：$\varepsilon \to \color{red}{\texttt{1}}\texttt{}\color{red}{\texttt{0}} \to \color{red}{\texttt{0}}\texttt{10}\color{red}{\texttt{1}} \to \color{red}{\texttt{1}}\texttt{0101}\color{red}{\texttt{0}}$。

在第五个测试用例中，Timur 起始的最短可能字符串是 $\texttt{101}$，他执行了如下操作：$\texttt{101} \to \color{red}{\texttt{0}}\texttt{101}\color{red}{\texttt{1}} \to \color{red}{\texttt{1}}\texttt{01011}\color{red}{\texttt{0}}$。