CF1469E.A Bit Similar

Let's call two strings $a$ and $b$ (both of length $k$) a bit similar if they have the same character in some position, i. e. there exists at least one $i \in [1, k]$ such that $a_i = b_i$.

You are given a binary string $s$ of length $n$ (a string of $n$ characters 0 and/or 1) and an integer $k$. Let's denote the string $s[i..j]$ as the substring of $s$ starting from the $i$-th character and ending with the $j$-th character (that is, $s[i..j] = s_i s_{i + 1} s_{i + 2} \dots s_{j - 1} s_j$).

Let's call a binary string $t$ of length $k$ beautiful if it is a bit similar to all substrings of $s$ having length exactly $k$; that is, it is a bit similar to $s[1..k], s[2..k+1], \dots, s[n-k+1..n]$.

Your goal is to find the lexicographically smallest string $t$ that is beautiful, or report that no such string exists. String $x$ is lexicographically less than string $y$ if either $x$ is a prefix of $y$ (and $x \ne y$), or there exists such $i$ ($1 \le i \le \min(|x|, |y|)$), that $x_i \lt y_i$, and for any $j$ ($1 \le j \lt i$) $x_j = y_j$.

我们称两个长度均为 $k$ 的字符串 $a$ 和 $b$ 是位相似的（bit similar），如果它们在某个位置上的字符相同，即存在至少一个 $i \in [1, k]$，使得 $a_i = b_i$。

给定一个长度为 $n$ 的二进制字符串 $s$（由 $n$ 个字符 0 和/或 1 组成）以及一个整数 $k$。记 $s[i..j]$ 表示 $s$ 中从第 $i$ 个字符开始、到第 $j$ 个字符结束的子串（即 $s[i..j] = s_i s_{i + 1} s_{i + 2} \dots s_{j - 1} s_j$）。

我们称一个长度为 $k$ 的二进制字符串 $t$ 是优美的（beautiful），如果它与 $s$ 中所有长度恰好为 $k$ 的子串均位相似；即 $t$ 与 $s[1..k], s[2..k+1], \dots, s[n-k+1..n]$ 均位相似。

你的目标是找出字典序最小的优美的字符串 $t$；若不存在这样的字符串，则报告不存在。字符串 $x$ 的字典序小于字符串 $y$，当且仅当：(1) $x$ 是 $y$ 的真前缀（即 $x \ne y$ 且 $x$ 是 $y$ 的前缀），或 (2) 存在某个 $i$（$1 \le i \le \min(|x|, |y|)$），使得 $x_i \lt y_i$，且对任意 $j$（$1 \le j \lt i$）都有 $x_j = y_j$。

The first line contains one integer $q$ ($1 \le q \le 10000$) — the number of test cases. Each test case consists of two lines.

The first line of each test case contains two integers $n$ and $k$ ($1 \le k \le n \le 10^6$). The second line contains the string $s$, consisting of $n$ characters (each character is either 0 or 1).

It is guaranteed that the sum of $n$ over all test cases does not exceed $10^6$.

第一行包含一个整数 $q$（$1 \le q \le 10000$），表示测试用例的数量。每个测试用例由两行组成。

每个测试用例的第一行包含两个整数 $n$ 和 $k$（$1 \le k \le n \le 10^6$）。第二行包含一个长度为 $n$ 的字符串 $s$，其中每个字符均为 0 或 1。

保证所有测试用例的 $n$ 之和不超过 $10^6$。

For each test case, print the answer as follows:

• if it is impossible to construct a beautiful string, print one line containing the string NO (note: exactly in upper case, you can't print No, for example);
• otherwise, print two lines. The first line should contain the string YES (exactly in upper case as well); the second line — the lexicographically smallest beautiful string, consisting of $k$ characters 0 and/or 1.

对于每个测试用例，请按如下方式输出答案：

• 如果无法构造出优美的字符串，则输出一行字符串 NO（注意：必须严格为大写，例如不能输出 No）；
• 否则，输出两行。第一行应为字符串 YES（同样必须严格为大写）；第二行为字典序最小的优美字符串，该字符串由 $k$ 个字符 0 和/或 1 组成。