CodingHardcod-g812

Subject Rolling hashLevel Senior–Staff~40 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given a lowercase string s, return the longest substring that appears at least twice in s (occurrences may overlap). If none repeats, return the empty string. For 'banana' the answer is 'ana'. If multiple longest answers exist, returning any one of them is acceptable. Length up to a few thousand.

Implement

longest_dup_substring(s: str) → str

Examples

in["banana"]out"ana"

What a strong answer looks like

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.

Learn the concepts

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.

Run or narrate your approach, then ask the coach.