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Use a stack to handle nested encoded strings. Iterate through the input, building the current string and multiplier, and when encountering '[', push the current state onto the stack and reset; when encountering ']', pop and combine. Finally, return the decoded string.
Pro tip: Clarify constraints upfront (e.g., k is a positive integer, input is always valid) and discuss time/space complexity. Mention that a recursive approach is also possible but iterative with a stack is often more efficient and avoids recursion depth issues.
Restate the problem to ensure clarity. Ask about constraints: maximum k, nesting depth, input validity, and character set. Consider edge cases like empty string, no encoding, or multiple encodings.
Decide between stack-based iterative or recursive approach. Explain why stack is suitable for nested structures. Outline how to maintain current string and repeat count.
Trace the algorithm on a sample input like '3[a2[c]]' to demonstrate correctness. Show how the stack evolves and how strings are combined.
State time and space complexity. Discuss potential optimizations, such as using a StringBuilder for efficient string concatenation.
Write clean code with meaningful variable names. Test with provided examples and edge cases. Be prepared to debug if needed.
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