CF1369B.AccurateLee

Lee was cleaning his house for the party when he found a messy string under the carpets. Now he'd like to make it clean accurately and in a stylish way...

The string $s$ he found is a binary string of length $n$ (i. e. string consists only of 0-s and 1-s).

In one move he can choose two consecutive characters $s_i$ and $s_{i+1}$, and if $s_i$ is 1 and $s_{i + 1}$ is 0, he can erase exactly one of them (he can choose which one to erase but he can't erase both characters simultaneously). The string shrinks after erasing.

Lee can make an arbitrary number of moves (possibly zero) and he'd like to make the string $s$ as clean as possible. He thinks for two different strings $x$ and $y$, the shorter string is cleaner, and if they are the same length, then the lexicographically smaller string is cleaner.

Now you should answer $t$ test cases: for the $i$-th test case, print the cleanest possible string that Lee can get by doing some number of moves.

Small reminder: if we have two strings $x$ and $y$ of the same length then $x$ is lexicographically smaller than $y$ if there is a position $i$ such that $x_1 = y_1$, $x_2 = y_2$,..., $x_{i - 1} = y_{i - 1}$ and $x_i \lt y_i$.

Lee 在为聚会打扫房间时，在地毯下发现了一串混乱的字符串。现在他希望以一种精确而时尚的方式将其清理干净……

他发现的字符串 $s$ 是一个长度为 $n$ 的二进制字符串（即仅由 0 和 1 构成的字符串）。

在一次操作中，他可以选择两个相邻的字符 $s_i$ 和 $s_{i+1}$；若 $s_i = 1$ 且 $s_{i + 1} = 0$，则他可以恰好删除其中的一个字符（他可任选删除哪一个，但不能同时删除两个字符）。删除后字符串会缩短。

Lee 可以执行任意次数（包括零次）的操作，他希望将字符串 $s$ 清理得尽可能“干净”。他认为：对于两个不同的字符串 $x$ 和 $y$，长度更短的字符串更干净；若长度相同，则字典序更小的字符串更干净。

现在你需要回答 $t$ 组测试用例：对第 $i$ 个测试用例，输出 Lee 经过若干次操作后所能得到的最干净的字符串。

小提示：若两个字符串 $x$ 和 $y$ 长度相同，则当存在某个位置 $i$，使得 $x_1 = y_1$, $x_2 = y_2$, …, $x_{i - 1} = y_{i - 1}$ 且 $x_i \lt y_i$ 时，称 $x$ 的字典序小于 $y$。

The first line contains the integer $t$ ($1 \le t \le 10^4$) — the number of test cases.

Next $2t$ lines contain test cases — one per two lines.

The first line of each test case contains the integer $n$ ($1 \le n \le 10^5$) — the length of the string $s$.

The second line contains the binary string $s$. The string $s$ is a string of length $n$ which consists only of zeroes and ones.

It's guaranteed that sum of $n$ over test cases doesn't exceed $10^5$.

第一行包含一个整数 $t$（$1 \le t \le 10^4$）—— 表示测试用例的数量。

接下来的 $2t$ 行包含测试用例 —— 每两个行为一个测试用例。

每个测试用例的第一行包含一个整数 $n$（$1 \le n \le 10^5$）—— 表示字符串 $s$ 的长度。

每个测试用例的第二行包含一个二进制字符串 $s$。字符串 $s$ 是一个长度为 $n$ 的字符串，仅由字符 0 和 1 组成。

保证所有测试用例的 $n$ 之和不超过 $10^5$。

Print $t$ answers — one per test case.

The answer to the $i$-th test case is the cleanest string Lee can get after doing some number of moves (possibly zero).

输出 $t$ 个答案——每个测试用例对应一个答案。

第 $i$ 个测试用例的答案是 Lee 在进行若干次（可能为零次）操作后所能得到的最“干净”的字符串。

In the first test case, Lee can't perform any moves.

In the second test case, Lee should erase $s_2$.

In the third test case, Lee can make moves, for example, in the following order: 11001101 $\rightarrow$ 1100101 $\rightarrow$ 110101 $\rightarrow$ 10101 $\rightarrow$ 1101 $\rightarrow$ 101 $\rightarrow$ 01.

在第一个测试用例中，Lee 无法进行任何操作。

在第二个测试用例中，Lee 应当删除 $s_2$。

在第三个测试用例中，Lee 可以进行若干次操作，例如按如下顺序：11001101 $\rightarrow$ 1100101 $\rightarrow$ 110101 $\rightarrow$ 10101 $\rightarrow$ 1101 $\rightarrow$ 101 $\rightarrow$ 01。