public class Solution
extends Object
2014 - Longest Subsequence Repeated k Times\.
Hard
You are given a string `s` of length `n`, and an integer `k`. You are tasked to find the **longest subsequence repeated** `k` times in string `s`.
A **subsequence** is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.
A subsequence `seq` is **repeated** `k` times in the string `s` if `seq * k` is a subsequence of `s`, where `seq * k` represents a string constructed by concatenating `seq` `k` times.
* For example, `"bba"` is repeated `2` times in the string `"bababcba"`, because the string `"bbabba"`, constructed by concatenating `"bba"` `2` times, is a subsequence of the string `"**b**a**bab**c**ba**"`.
Return _the **longest subsequence repeated**_ `k` _times in string_ `s`_. If multiple such subsequences are found, return the **lexicographically largest** one. If there is no such subsequence, return an **empty** string_.
**Example 1:**
**Input:** s = "letsleetcode", k = 2
**Output:** "let"
**Explanation:** There are two longest subsequences repeated 2 times: "let" and "ete". "let" is the lexicographically largest one.
**Example 2:**
**Input:** s = "bb", k = 2
**Output:** "b"
**Explanation:** The longest subsequence repeated 2 times is "b".
**Example 3:**
**Input:** s = "ab", k = 2
**Output:** ""
**Explanation:** There is no subsequence repeated 2 times. Empty string is returned.
**Constraints:**
* `n == s.length`
* `2 <= n, k <= 2000`
* `2 <= n < k * 8`
* `s` consists of lowercase English letters.