CF1925A.We Got Everything Covered!

You are given two positive integers $n$ and $k$.

Your task is to find a string $s$ such that all possible strings of length $n$ that can be formed using the first $k$ lowercase English alphabets occur as a subsequence of $s$.

If there are multiple answers, print the one with the smallest length. If there are still multiple answers, you may print any of them.

Note: A string $a$ is called a subsequence of another string $b$ if $a$ can be obtained by deleting some (possibly zero) characters from $b$ without changing the order of the remaining characters.

给你两个正整数 $n$ 和 $k$。

你的任务是构造一个字符串 $s$，使得由前 $k$ 个小写英文字母所能构成的所有长度为 $n$ 的字符串，均作为 $s$ 的子序列出现。

如果存在多个满足条件的答案，请输出长度最短的那个；若仍存在多个长度最短的答案，你可以输出其中任意一个。

注意：若字符串 $a$ 可通过从字符串 $b$ 中删除若干（可能为零）个字符、且不改变剩余字符的相对顺序而得到，则称 $a$ 是 $b$ 的子序列。

The first line of input contains a single integer $t$ ($1\leq t\leq 676$) denoting the number of test cases.

Each test case consists of a single line of input containing two integers $n$ ($1\leq n\leq 26$) and $k$ ($1\leq k\leq 26$).

输入的第一行包含一个整数 $t$（$1\leq t\leq 676$），表示测试用例的数量。

每个测试用例由一行输入组成，包含两个整数 $n$（$1\leq n\leq 26$）和 $k$（$1\leq k\leq 26$）。

For each test case, print a single line containing a single string $s$ which satisfies the above property. If there are multiple answers, print the one with the smallest length. If there are still multiple answers, you may print any of them.

对于每个测试用例，输出一行，包含一个满足上述性质的字符串 $s$。如果存在多个答案，输出长度最小的那个；如果仍存在多个答案，你可以输出其中任意一个。

For the first test case, there are two strings of length $1$ which can be formed using the first $2$ lowercase English alphabets, and they are present in $s$ as a subsequence as follows:

• $\texttt{a}: {\color{red}{\texttt{a}}}\texttt{b}$
• $\texttt{b}: \texttt{a}{\color{red}{\texttt{b}}}$

For the second test case, there is only one string of length $2$ which can be formed using the first lowercase English alphabet, and it is present in $s$ as a subsequence as follows:

• $\texttt{aa}: {\color{red}{\texttt{aa}}}$

For the third test case, there are $4$ strings of length $2$ which can be formed using the first $2$ lowercase English alphabets, and they are present in $s$ as a subsequence as follows:

• $\texttt{aa}: \texttt{b}{\color{red}{\texttt{aa}}}\texttt{b}$
• $\texttt{ab}: \texttt{ba}{\color{red}{\texttt{ab}}}$
• $\texttt{ba}: {\color{red}{\texttt{ba}}}\texttt{ab}$
• $\texttt{bb}: {\color{red}{\texttt{b}}}\texttt{aa}{\color{red}{\texttt{b}}}$

For the fourth test case, there are $9$ strings of length $2$ which can be formed using the first $3$ lowercase English alphabets, and they are present in $s$ as a subsequence as follows:

• $\texttt{aa}: {\color{red}{\texttt{a}}}\texttt{bcb}{\color{red}{\texttt{a}}}\texttt{c}$
• $\texttt{ab}: {\color{red}{\texttt{ab}}}\texttt{cbac}$
• $\texttt{ac}: \texttt{abcb}{\color{red}{\texttt{ac}}}$
• $\texttt{ba}: \texttt{abc}{\color{red}{\texttt{ba}}}\texttt{c}$
• $\texttt{bb}: \texttt{a}{\color{red}{\texttt{b}}}\texttt{c}{\color{red}{\texttt{b}}}\texttt{ac}$
• $\texttt{bc}: \texttt{a}{\color{red}{\texttt{bc}}}\texttt{bac}$
• $\texttt{ca}: \texttt{ab}{\color{red}{\texttt{c}}}\texttt{b}{\color{red}{\texttt{a}}}\texttt{c}$
• $\texttt{cb}: \texttt{ab}{\color{red}{\texttt{cb}}}\texttt{ac}$
• $\texttt{cc}: \texttt{ab}{\color{red}{\texttt{c}}}\texttt{ba}{\color{red}{\texttt{c}}}$

对于第一个测试用例，使用前 $2$ 个小写英文字母可以构造出两个长度为 $1$ 的字符串，且它们均作为子序列出现在 $s$ 中，具体如下：

• $\texttt{a}: {\color{red}{\texttt{a}}}\texttt{b}$
• $\texttt{b}: \texttt{a}{\color{red}{\texttt{b}}}$

对于第二个测试用例，仅存在一个长度为 $2$ 的字符串，它由第一个小写英文字母构成，且该字符串作为子序列出现在 $s$ 中，具体如下：

• $\texttt{aa}: {\color{red}{\texttt{aa}}}$

对于第三个测试用例，使用前 $2$ 个小写英文字母可以构造出 $4$ 个长度为 $2$ 的字符串，且它们均作为子序列出现在 $s$ 中，具体如下：

• $\texttt{aa}: \texttt{b}{\color{red}{\texttt{aa}}}\texttt{b}$
• $\texttt{ab}: \texttt{ba}{\color{red}{\texttt{ab}}}$
• $\texttt{ba}: {\color{red}{\texttt{ba}}}\texttt{ab}$
• $\texttt{bb}: {\color{red}{\texttt{b}}}\texttt{aa}{\color{red}{\texttt{b}}}$

对于第四个测试用例，使用前 $3$ 个小写英文字母可以构造出 $9$ 个长度为 $2$ 的字符串，且它们均作为子序列出现在 $s$ 中，具体如下：

• $\texttt{aa}: {\color{red}{\texttt{a}}}\texttt{bcb}{\color{red}{\texttt{a}}}\texttt{c}$
• $\texttt{ab}: {\color{red}{\texttt{ab}}}\texttt{cbac}$
• $\texttt{ac}: \texttt{abcb}{\color{red}{\texttt{ac}}}$
• $\texttt{ba}: \texttt{abc}{\color{red}{\texttt{ba}}}\texttt{c}$
• $\texttt{bb}: \texttt{a}{\color{red}{\texttt{b}}}\texttt{c}{\color{red}{\texttt{b}}}\texttt{ac}$
• $\texttt{bc}: \texttt{a}{\color{red}{\texttt{bc}}}\texttt{bac}$
• $\texttt{ca}: \texttt{ab}{\color{red}{\texttt{c}}}\texttt{b}{\color{red}{\texttt{a}}}\texttt{c}$
• $\texttt{cb}: \texttt{ab}{\color{red}{\texttt{cb}}}\texttt{ac}$
• $\texttt{cc}: \texttt{ab}{\color{red}{\texttt{c}}}\texttt{ba}{\color{red}{\texttt{c}}}$