CF1864B.Swap and Reverse

传统题 时间 2000 ms 内存 256 MiB 5 尝试 1 已通过 1 标签

Swap and Reverse

You are given a string ss of length nn consisting of lowercase English letters, and an integer kk. In one step you can perform any one of the two operations below:

  • Pick an index ii (1in21 \le i \le n - 2) and swap sis_{i} and si+2s_{i+2}.
  • Pick an index ii (1ink+11 \le i \le n-k+1) and reverse the order of letters formed by the range [i,i+k1][i,i+k-1] of the string. Formally, if the string currently is equal to $s_1\ldots s_{i-1}s_is_{i+1}\ldots s_{i+k-2}s_{i+k-1}s_{i+k}\ldots s_{n-1}s_n$, change it to $s_1\ldots s_{i-1}s_{i+k-1}s_{i+k-2}\ldots s_{i+1}s_is_{i+k}\ldots s_{n-1}s_n$.

You can make as many steps as you want (possibly, zero). Your task is to find the lexicographically smallest string you can obtain after some number of steps.

A string aa is lexicographically smaller than a string bb of the same length if and only if the following holds:

  • in the first position where aa and bb differ, the string aa has a letter that appears earlier in the alphabet than the corresponding letter in bb.

Input

Each test contains multiple test cases. The first line contains the number of test cases tt (1t1041 \le t \le 10^4). The description of the test cases follows.

The first line of each test case contains two integers nn and kk (1k<n1051 \le k \lt n \le 10^5).

The second line of each test case contains the string ss of length nn consisting of lowercase English letters.

It is guaranteed that the sum of nn over all test cases does not exceed 10510^5.

Output

For each test case, print the lexicographically smallest string after doing some (possibly, zero) steps.

Note

In the first test case, we can obtain the string "aimn" using the following operations:

  1. Reverse the range [3,4][3,4]. The string turns into "niam".
  2. Swap s1s_1 and s3s_3. The string turns into "ainm".
  3. Reverse the range [3,4][3,4]. The string turns into "aimn".

It can be proven that we cannot obtain any string lexicographically smaller than "aimn". Therefore, "aimn" is the answer.

In the second test case, we can obtain the string "aandp" using the following operations:

  1. Swap s3s_3 and s5s_5. The string turns into "paadn".
  2. Swap s1s_1 and s3s_3. The string turns into "aapdn".
  3. Swap s3s_3 and s5s_5. The string turns into "aandp".

It can be proven that we cannot obtain any string lexicographically smaller than "aandp". Therefore, "aandp" is the answer.

Samples

5
4 2
nima
5 3
panda
9 2
theforces
7 3
amirfar
6 4
rounds
aimn
aandp
ceefhorst
aafmirr
dnorsu

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