Lazy-Deletion

Circular queues, zigzag iterators, FIFO matching with cancellation, and the data structure combinations that design problems keep using

LeetCode 716 note: store unique ids on both the stack and the heap, record deletions by id, and discard deleted entries lazily; tracking values cannot tell duplicates apart

LeetCode 3885 note: a dict of current priorities plus a max-heap with lazy deletion, validated on pop

LeetCode 3829 note: one queue each for riders and drivers; cancellations only update a set, and canceled riders at the front are dropped before matching

LeetCode 3815 note: one max-heap per item, push a new entry on every bid change, and drop stale entries on query

LeetCode 3607 note: Union-Find groups, one min-heap per group, and lazy deletion for offline stations