200970: [AtCoder]ARC097 C - K-th Substring

Memory Limit:1024 MB Time Limit:2 S
Judge Style:Text Compare Creator:
Submit:0 Solved:0

Description

Score : $300$ points

Problem Statement

You are given a string $s$. Among the different substrings of $s$, print the $K$-th lexicographically smallest one.

A substring of $s$ is a string obtained by taking out a non-empty contiguous part in $s$. For example, if $s$ $=$ ababc, a, bab and ababc are substrings of $s$, while ac, z and an empty string are not. Also, we say that substrings are different when they are different as strings.

Let $X = x_{1}x_{2}...x_{n}$ and $Y = y_{1}y_{2}...y_{m}$ be two distinct strings. $X$ is lexicographically larger than $Y$ if and only if $Y$ is a prefix of $X$ or $x_{j} > y_{j}$ where $j$ is the smallest integer such that $x_{j} \neq y_{j}$.

Constraints

  • $1$ $≤$ $|s|$ $≤$ $5000$
  • $s$ consists of lowercase English letters.
  • $1$ $≤$ $K$ $≤$ $5$
  • $s$ has at least $K$ different substrings.

Partial Score

  • $200$ points will be awarded as a partial score for passing the test set satisfying $|s|$ $≤$ $50$.

Input

Input is given from Standard Input in the following format:

$s$
$K$

Output

Print the $K$-th lexicographically smallest substring of $K$.


Sample Input 1

aba
4

Sample Output 1

b

$s$ has five substrings: a, b, ab, ba and aba. Among them, we should print the fourth smallest one, b. Note that we do not count a twice.


Sample Input 2

atcoderandatcodeer
5

Sample Output 2

andat

Sample Input 3

z
1

Sample Output 3

z

Input

题意翻译

## Description 给定一个字符串 $S$,在 $S$ 的所有 ***互不相同的*** 非空字串中找出其中找到字典序第 $K$ 小的字串并输出。换句话说,就是找出 $S$ 所有的非空字串,按字典序升序排序, ***去重*** 后再选出第 $K$ 个。 ## Input 第一行,一个字符串 $S$ ; 第二行,一个整数 $K$ 。 ## Output 一个字符串表示答案。 ## Hint - $1\le |S|\le 5\times 10^3$ - $K\in [1,5]$ 其中 $S$ 只含有小写字母,保证 $S$ 中含有 $K$ 个不同的非空字串。 Translated by @[```_Wallace_```](https://www.luogu.com.cn/user/61430)

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