The basic case was fine, I traced through '3[a]2[bc]' pretty quickly with a stack.
Use a stack to handle nested encodings: push current string and repeat count when encountering '[', and pop and combine when encountering ']'. Iterate through the string, building the decoded result incrementally.
Pro tip: Clarify constraints upfront (e.g., input validity, character set, max depth) to avoid edge-case failures, and mention that a recursive solution is also possible but a stack-based iterative approach avoids recursion depth limits.
Restate the problem, confirm input format, and discuss edge cases like multi-digit numbers, nested brackets, and empty strings.
Decide between stack-based iterative or recursive approach; explain why stack is suitable for nested structures.
Trace through '3[a2[c]]' step-by-step, showing how the stack manages counts and strings.
State time and space complexity (O(n) time, O(n) space) and mention potential optimizations like using a StringBuilder.
Mention testing with cases like '2[abc]3[cd]ef', '10[a]', and nested deep structures to ensure correctness.
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