CodingMediumcod-g619

Subject String parsingLevel Mid–Senior~24 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Decode a run-length-style string with nesting of the form k[encoded], where the bracketed substring is repeated k times. k is a positive integer; brackets may nest. The input is always valid and contains only digits, lowercase letters, and square brackets. 1 <= len(s) <= 30000. Example: '3[a2[c]]' -> 'accaccacc'.

Implement

decode_string(s: str) → str

Examples

in["3[a2[c]]"]out"accaccacc"

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.