CodingHardcod-g378

Subject PalindromesLevel Senior–Staff~35 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given a string s of lowercase letters (0 <= len(s) <= 1000), return the number of DISTINCT non-empty palindromic subsequences of s, modulo 1_000_000_007. Two subsequences are different if their resulting strings differ (distinct by value, not by index set).

Implement

count_palindromic_subsequences(s: str) → int

Examples

in["bccb"]out6

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.