Αποτελέσματα Αναζήτησης
•APriority Queue ranks its elements by key with a total order relation • Keys: - Every element has its own key - Keys are not necessarily unique • Total Order Relation - Denoted by≤ -Reflexive: k ≤k -Antisymetric: if k1≤k2and k2≤k1, then k1≤k2. -Transitive: if k1≤k2and k2≤k3, then k1≤k3.
Heaps and Priority Queues • Heap can be used to implement a priority queue • store a (key, element) item at each internal node • keep track of the last node (2, Chomu) (5, Ram) (6, Sohan) (9, Shyam) (7, Anna)
Priority queues are used in a number of applications. We name three: In event-driven simulations, events can be kept in a priority queue, with the priority being the time at which an event is to take place. Events are removed from the queue in chronological order and processed.
26 Νοε 2024 · PriorityQueue (Comparator<E> comparator): Creates a PriorityQueue with the default initial capacity and whose elements are ordered according to the specified comparator. Example: The example below explains the following basic operations of the priority queue.
Use a priority queue. public UnorderedPQ(int maxN) { pq = (Item[]) new Comparable[maxN]; } public boolean isEmpty() { return N == 0; } public void insert(Item x) { pq[N++] = x; } public Item delMax() { int max = 0; for (int i = 1; i < N; i++) if (less(max, i)) max = i; exch(max, N-1); return pq[--N]; } } Challenge.
Priority Queue A priority queue (PQ for short) is a data structure that allows us to process keys in order, without storing them in full sorted order all at once
Priority Queue Client Example Problem: Find the largest M of a stream of N elements. Ex 1: Fraud detection - isolate $$ transactions. Ex 2: File maintenance – find biggest files or directories. Possible constraint: may not have enough memory to store N elements. Solution: Use a priority queue. Ex: top 10,000 in a stream of 1 billion.
