CodingMediumcod-g377

Subject KmpLevel Mid–Senior~20 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

A 'happy prefix' is a non-empty prefix of a string that is also a (proper) suffix, excluding the whole string itself. Given a string s of lowercase letters (1 <= len(s) <= 10^5), return the longest happy prefix. Return the empty string if none exists.

Implement

longest_happy_prefix(s: str) → str

Examples

in["level"]out"l"

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.