CodingMediumcod-g809

Subject KmpLevel Mid–Senior~25 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given a lowercase string s, return the length of the longest proper prefix of s that is also a suffix of s (a proper prefix excludes the whole string). For 'ababab' the answer is 4 ('abab'). For 'abcdef' it is 0. Length up to a few thousand.

Implement

longest_prefix_suffix(s: str) → int

Examples

in["ababab"]out4

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.