Harbour.Space Scholarship Contest 2023-2024 (Div. 1 + Div. 2)
B
Swap and Reverse
Codeforces
1100
原题
← AC →
翻译中…

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

翻译中…
  • Pick an index $i$ ($1 \le i \le n - 2$) and swap $s_{i}$ and $s_{i+2}$.
  • Pick an index $i$ ($1 \le i \le n-k+1$) and reverse the order of letters formed by the range $[i,i+k-1]$ 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 $s_1\ldots s_{i-1}s_{i+k-1}s_{i+k-2}\ldots s_{i+1}s_is_{i+k}\ldots s_{n-1}s_n$.
翻译中…

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.

翻译中…

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

翻译中…
  • in the first position where $a$ and $b$ differ, the string $a$ has a letter that appears earlier in the alphabet than the corresponding letter in $b$.
翻译中…

Input

翻译中…

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

翻译中…

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

翻译中…

The second line of each test case contains the string $s$ of length $n$ consisting of lowercase English letters.

翻译中…

It is guaranteed that the sum of $n$ over all test cases does not exceed $10^5$.

翻译中…

Output

翻译中…

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

翻译中…

Note

翻译中…

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

翻译中…
  1. Reverse the range $[3,4]$. The string turns into "niam".
  2. Swap $s_1$ and $s_3$. The string turns into "ainm".
  3. Reverse the range $[3,4]$. The string turns into "aimn".
翻译中…

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

翻译中…

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

翻译中…
  1. Swap $s_3$ and $s_5$. The string turns into "paadn".
  2. Swap $s_1$ and $s_3$. The string turns into "aapdn".
  3. Swap $s_3$ and $s_5$. The string turns into "aandp".
翻译中…

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

翻译中…

样例

Input #1
5
4 2
nima
5 3
panda
9 2
theforces
7 3
amirfar
6 4
rounds
Output #1
aimn
aandp
ceefhorst
aafmirr
dnorsu
InputCopy OutputCopy
题目信息
题号
1864B
时间限制
1 s
内存限制
256 MB
标签
构造
贪心
排序
字符串

题面与样例版权归 Codeforces 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。