The example makes it look straightforward but I spent way too long second-guessing whether to use a set for seen IDs or try to be clever with ordering.
Clarify the requirements and constraints first, then propose an iterator that lazily yields elements from favorites followed by photos, using a seen set to deduplicate and a blocked set to skip. Discuss trade-offs between memory and time, and handle edge cases like empty lists or all elements blocked.
Pro tip: Emphasize lazy evaluation and early termination to handle large or infinite streams efficiently, and mention that using a hash set for seen IDs gives O(1) average lookup, which is crucial for performance.
Ask about input types, whether lists can be modified, if blocked IDs are provided as a set, and if duplicates within a single list are possible. Confirm the expected order and behavior when all elements are blocked.
Propose a class with a constructor that takes favorites, photos, and blocked IDs. Maintain an index for the current list, a flag for which list is active, and a seen set to track yielded IDs.
In next(), advance through the current list, skipping blocked or seen IDs, and switch to the next list when exhausted. hasNext() should peek ahead to check if any valid element remains without consuming it.
State that each element is processed at most once, so time complexity is O(n) where n is total elements, and space complexity is O(k) for the seen set, where k is the number of unique yielded elements.
Mention alternatives like using a generator or merging on the fly, and how to handle memory constraints if the seen set grows too large. Also consider thread-safety if needed.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.