Longest Subsequence Repeated k Times

Given string s and integer k, find the longest subsequence of s that can be repeated k times to form a string that is a subsequence of s.

Examples
Input: ["letsleetcode",2]
Output: "let"
Hints

Longest Subsequence Repeated k Times

Given string s and integer k, find the longest subsequence of s that can be repeated k times to form a string that is a subsequence of s.