使 Java PriorityQueue 成为稳定的优先级队列 [英] Making a Java PriorityQueue into a stable priority queue

问题描述

我正在尝试用 Java 实现一个稳定的(先进先出)优先级队列.假设键是名字，值是年龄，我知道我可以像这样制作一个不稳定的优先级队列:

I'm trying to implement a stable (first in first out) priority queue in Java. Supposing that the key is a name and the value is an age, I know I can make an unstable priority queue like this:

Queue<Map.Entry<String, Integer>> pq = new PriorityQueue<Map.Entry<String, Integer>>(100, ageComparator);

这几乎完成了我需要它做的所有事情，只是它在我插入(或删除它们)时不保持键值对的顺序.

This does pretty much everything that I need it to, except that it doesn't maintain order of key-value pairs as I insert them (or remove them).

我通过制作 LinkedList 找到了一种变通办法"，它提供了基本上所有相同的功能，只是它不包含带有比较器选项的构造函数，而且我觉得它必须更慢，因为我通过在每个队列操作之后调用 Collections.sort() 来维护值排序.

I've found a "work around" by making a LinkedList, which offers essentially all of the same functionality, except that it doesn't include a constructor with a comparator option, and I feel that it must be slower since I maintain value ordering by calling Collections.sort() after each queue operation.

所以我想确实有两个我感兴趣的选项.首先，我如何编辑上面的 PriorityQueue 以保持插入和删除顺序?或者第二，如何强制我的 LinkedList 选项立即使用比较器，而不必对每个操作调用排序?谢谢！

So I guess that really there are two options that I'm interested in. First, how could I edit the PriorityQueue above to maintain insertion and removal order? Or second, how could I force my LinkedList option to use a comparator immediately rather than having to call a sort on each operation? Thanks!

感谢在发布的第一条评论中提出的好问题.FIFO，我的意思是对于具有相等值的键值对，应该先提取最先放入的键值对.

Thanks for the good question in the first comment that was posted. By FIFO, I mean that for key-value pairs with equal values, the pair which is put in first should be extracted first.

推荐答案

你需要这样的东西:

import java.util.AbstractMap;
import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.concurrent.atomic.AtomicInteger;

public class PriorityTest {
  @SuppressWarnings("serial")
  private static class Entry extends AbstractMap.SimpleEntry<String, Integer> {
    private final static AtomicInteger seq = new AtomicInteger(0);
    final int order;
    public Entry(final String _key, final Integer _value) {
      super(_key, _value);
      order = seq.incrementAndGet();
    }
  }

  private static class OrderedComparator implements Comparator<Entry> {
    @Override
    public int compare(final Entry _e1, final Entry _e2) {
      int r = _e1.getValue().compareTo(_e2.getValue());
      if (r == 0)
        return Integer.compare(_e1.order, _e2.order);
      return r;
    }
  }

  public static void main(String[] args) {
    final PriorityQueue<Entry> pq = new PriorityQueue<Entry>(10, new OrderedComparator());
    pq.add(new Entry("Jane", 22));
    pq.add(new Entry("John", 15));
    pq.add(new Entry("Bill", 45));
    pq.add(new Entry("Bob", 22));
    while(!pq.isEmpty()) {
      System.out.println(pq.remove());
    }
  }
}

这篇关于使 Java PriorityQueue 成为稳定的优先级队列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！