CodingHardcod-g522

Subject Dynamic programming 2dLevel Senior–Staff~25 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given strings s and t, count the number of distinct subsequences of s that equal t. A subsequence keeps relative order but may drop characters. The count fits in a 64-bit integer. Either string may be empty; the empty string is a subsequence of any string exactly once.

Implement

distinct_subseq(s: str, t: str) → int

Examples

in["rabbbit","rabbit"]out3

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.