My first instinct was a min-heap keyed on timestamp, which is the right call, but I fumbled explaining why you need to reschedule the system timer every time setNewTimer is called with something earlier than the current head.
Clarify the problem constraints and then propose a min-heap of timers keyed by expiration time, with a single underlying system timer set to the earliest expiration. Explain how to handle duplicate timestamps and overrides, and analyze time complexity for insertion and firing.
Pro tip: Mention that using a min-heap allows O(log n) insertion and O(1) peek for the next timer, and that you can optimize duplicate timestamps by grouping them in a list at the same heap node to avoid redundant system timer resets.
Ask about the expected number of timers, whether timers can be cancelled, and the behavior for duplicate timestamps or overrides. Confirm that only one system timer can be active at a time.
Propose a min-heap (priority queue) ordered by expiration timestamp, where each node stores the timestamp and a list of callbacks for that time. This efficiently retrieves the earliest timer.
In setNewTimer, insert the timer into the heap; if it becomes the new minimum, reset the system timer to its expiration. In handleTimer, pop all expired timers (timestamp <= current time), fire their callbacks, and set the system timer to the next earliest expiration.
Address duplicate timestamps by grouping them in the same heap node, overrides by allowing cancellation (e.g., lazy deletion with a cancelled flag), and empty heap by clearing the system timer.
Insertion is O(log n), firing expired timers is O(k log n) where k is the number fired, and peeking is O(1). Discuss alternative structures like balanced BST or timing wheel for different trade-offs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.