Design a Set of Stacks with `popAt`
Implement a `SetOfStacks` data structure where a new stack is created once the previous one exceeds capacity. Implement a `popAt` operation that performs a pop on a specific sub-stack.
Why Interviewers Ask This
Adobe evaluates this question to assess a candidate's ability to design scalable data structures that handle memory fragmentation and edge cases. It tests understanding of array-based stack implementations, pointer manipulation across sub-structures, and the critical trade-off between strict capacity enforcement versus maintaining structural integrity during partial pops.
How to Answer This Question
1. Clarify requirements: Ask if popAt should shift elements from subsequent stacks to maintain balance or simply remove from the target index. 2. Define core structure: Propose an ArrayList or List of Stacks where each internal stack has a fixed capacity. 3. Implement push logic: Explain how to check if the current top stack is full before adding; if full, instantiate a new stack. 4. Design popAt logic: Detail retrieving the specific sub-stack, performing the pop, and handling the case where the popped stack becomes empty (optional cleanup). 5. Discuss complexity: Analyze time complexity for push (O(1)) and popAt (O(N) worst-case if shifting required), noting Adobe values efficiency in high-throughput environments like Creative Cloud.
Key Points to Cover
- Explicitly defining the behavior when a sub-stack becomes empty after a pop
- Clarifying whether elements must be shifted to maintain fullness constraints
- Demonstrating awareness of O(1) vs O(N) trade-offs in the popAt implementation
- Handling boundary conditions like invalid indices or empty collections gracefully
- Connecting the solution to real-world scalability needs typical of Adobe products
Sample Answer
To solve this, I would first define a SetOfStacks class containing a list of individual Stack objects, each with a defined capacity. For the push operation, I'd check if the last stack in the list has reached its limit.…
Common Mistakes to Avoid
- Failing to ask about the shifting requirement, leading to an incorrect assumption about data movement
- Implementing a single large array instead of a list of lists, missing the 'Set' concept entirely
- Ignoring edge cases where the requested index exceeds the number of available sub-stacks
- Not considering the memory overhead of creating too many small stack objects without a threshold
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