Question
Given a lowercase string s, return the lexicographically smallest DISTINCT substring that is the k-th smallest among all distinct non-empty substrings (1-indexed k). If k exceeds the number of distinct substrings, return the empty string. For s='aab', the sorted distinct substrings are 'a','aa','aab','ab','b'; k=3 gives 'aab'. Length up to a few hundred.
kth_distinct_substring(s: str, k: int) → str["aab",3]out"aab"State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.