CodingHardcod-g380

Subject StringsLevel Senior–Staff~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

A message of digits is encoded with 'A'->1 ... 'Z'->26. The string may also contain '*', a wildcard for any digit 1-9. Given such a string s (1 <= len(s) <= 10^5), return the number of ways to decode it, modulo 1_000_000_007. '0' alone cannot be decoded and only combines as part of 10 or 20 (but note 10/20 with '*' is handled by the digit cases here).

Implement

num_decodings_ii(s: str) → int

Examples

in["*"]out9

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.