CodingMediumcod-p050

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

Question

A message of digits is encoded where 'A'..'Z' map to '1'..'26'. Return the number of ways to decode it.

Implement

num_decodings(s: str) → int

Examples

in["12"]out2

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.