Design a nested-list iterator
Company: Adobe
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
You are given a nested structure that can contain integers or further lists. Design an iterator over this structure that returns integers in left-to-right order without pre-flattening the entire input. Implement a class NestedIterator with: constructor(nestedList), boolean hasNext(), and int next(). The iterator must use O(d) extra space where d is the maximum nesting depth, and hasNext()/next() should be amortized O(
1). Avoid recursion by using an explicit stack of iterators or indexes. Additionally, implement a recursive pre-flattening approach, compare both methods in time and space complexity, and discuss edge cases such as empty lists, deeply nested empty lists, and integer bounds.
Overview: This question evaluates the ability to implement an efficient iterator over nested lists, testing skills in iterator state management, lazy traversal, explicit stack usage, and algorithmic complexity reasoning.
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Return integers from a nested list in left-to-right order, equivalent to a lazy NestedIterator traversal.
Constraints
- Inputs are Python literals matching the function signature.
- Return a deterministic exact-match value.
Examples
Input: ([1,[2,[3]],4],)
Expected Output: [1, 2, 3, 4]
Explanation: Nested integers.
Input: ([[],[1,[]],2],)
Expected Output: [1, 2]
Explanation: Empty nested lists.
Hints
- Model object-style prompts as arrays or operation streams when needed.
- Handle empty and boundary cases before the main logic.