Implements a Priority Queue unordered that iterates over the largest key. - Java Data Structure

Java examples for Data Structure:queue

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Description

Implements a Priority Queue unordered that iterates over the largest key.

Demo Code

import static java.lang.System.out;

import java.util.NoSuchElementException;

public class UnorderedMaxPQ<Key extends Comparable<Key>> {

    private Key[] pq;
    private int N;
    //from  www  .  java2s.c  o  m
    public UnorderedMaxPQ() {
      this(1);
    }
    
    @SuppressWarnings("unchecked")    
    public UnorderedMaxPQ(int capacity) {
        pq = (Key[]) new Comparable[capacity];
    }
    
    public boolean isEmpty() {
        return N == 0;
    }
    
    public void insert(Key k) {
      if (N == pq.length - 1) 
          resize(2 * pq.length);
      
        pq[N++] = k;
    }
    
    //linear (N) running time
    public Key delMax() {
      if (isEmpty()) 
          throw new NoSuchElementException();
        
      int max = 0;
        for (int i = 1; i < N; i++)
            if (less(max, i))
                max = i;
        
        exch(max, N-1);
        Key k = pq[--N];
        pq[N] = null;
        
        if ((N > 0) && (N == (pq.length - 1) / 4)) 
            resize(pq.length  / 2);
        
        return k;
    }
    
    private boolean less(int i, int j) {
      return pq[i].compareTo(pq[j]) < 0;
    }
    
    private void exch(int i, int j) {
        Key swap = pq[i];
        pq[i] = pq[j];
        pq[j] = swap;
    }
    
    private void resize(int capacity) {
        @SuppressWarnings("unchecked")
        Key[] copy = (Key[]) new Comparable[capacity];
        
        for (int i = 0; i <= N; i++) 
            copy[i] = pq[i];
        
        pq = copy;
    }
    
    public static void main(String[] args) {
        UnorderedMaxPQ<String> queue = new UnorderedMaxPQ<String>(15);
        queue.insert("P");
        queue.insert("R");
        queue.insert("I");
        queue.insert("O");
        queue.insert("R");
        queue.insert("I");
        queue.insert("T");
        queue.insert("Y");
        queue.insert("Q");
        queue.insert("U");
        queue.insert("E");
        queue.insert("U");
        queue.insert("E");
        
        while (!queue.isEmpty()) {
            out.printf("%s ", queue.delMax());
        }
    }
}

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