Extend Queue: Min-Size & Min-Sum Selector

Extend a basic `Queue` class with two selectors over a collection of queues: find the queue with the minimum size, and find the queue with the minimum sum of elements. Tests data-structure design and operation-cost trade-off discussion. Requirements Given a basic Queue class supporting enqueue / dequeue, extend the surrounding container to support two additional operations over a collection of such queues: findQueueWithMinSize() — return the queue (or its index) with the smallest current length. findQueueWithMinSum() — return the queue (or its index) with the smallest current sum of elements. The interviewer expects a discussion of which auxiliary structures to maintain, and how each enqueue / dequeue updates them. Notes Naïve solution: scan all queues for each query. O(K) per query where K is the number of queues. Fine if K is small; flag the cost up-front. Maintain a Map<queueId, size> and a min-heap keyed by size, with lazy deletion of stale entries. Each enqueue / dequeue updates the map and pushes a new heap entry; queries pop stale entries until the top is fresh. Amortized O(log K). Same skeleton for findQueueWithMinSum — track (queueId, sum) and another min-heap. enqueue(v) adds v; dequeue subtracts the dequeued value (so each queue's dequeue must know which value left). Threading note: if the interviewer makes the container concurrent, the heap-with-lazy-deletion strategy needs a single mutex around the maps; the heap can stay outside the lock. A TreeMap<Integer, Set<queueId>> is a cleaner alternative to lazy-deletion heaps and is worth mentioning as an option. Preparation Sketch the public API first, then list which auxiliary structures back each method and what each enqueue / dequeue mutates. This problem is graded on discussion as much as code. Practice expressing the trade-off between "scan on query" (cheap writes, expensive reads) and "maintain aggregates" (expensive writes, cheap reads) — Goldman interviewers consistently ask candidates to choose and justify.