you give string s integer k letter letter integer repetitionReturn lexicographically smallest subsequence s length k letter letter appear repetition time the test case generate letter appear s repetition timesA subsequence string derive string delete character change order remain charactersA stre lexicographically small string b position b differ string letter appear early alphabet corresponding letter b example 1input s leet k 3 letter e repetition 1output eetExplanation there subsequence length 3 letter e appear 1 time lee leet let leet let leet eet leetthe lexicographically smallest subsequence eetExample 2input s leetcode k 4 letter e repetition 2output ecdeexplanation ecde lexicographically small subsequence length 4 letter e appear 2 timesexample 3input s bb k 2 letter b repetition 2Output bbexplanation bb subsequence length 2 letter b appear 2 time Constraints1 repetition k slength 5 104s consist lowercase english lettersletter lowercase english letter appear s repetition time