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Priority Queue
Not FIFO at all: the highest-priority element leaves first, regardless of arrival. Almost always implemented as a binary heap.
What to know
- The queue interface hides a heap: insert and extract are O(log n).
- Dijkstra, Prim, A*, Huffman, and k-way merge are all priority-queue algorithms.
- See the Heaps deep dive for the mechanics of the underlying structure.
In the wild: OS process schedulers, hospital triage, event-driven simulators, job queues with priorities.
Algorithms to reach for
Dijkstra with PQ
O((V+E) log V)Always expand the closest unsettled node
K-way merge
O(N log k)Merge k sorted lists by popping the smallest head
Huffman coding
O(n log n)Merge two rarest symbols repeatedly
Practice problems — with full guides
Each problem has its own page: progressive hints, how to approach it, and the full solution.