CodingHardcod-g614

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

Question

Given a string s, count the number of distinct non-empty palindromic SUBSEQUENCES in s, modulo 1000000007. Subsequences are distinguished by their character content (equal strings count once), not by index. 1 <= len(s) <= 1000, lowercase letters. Example: 'bccb' has palindromic subsequences b, c, cc, bb, bcb, bccb = 6.

Implement

count_distinct_palindromic_subseq(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.