Question

我正在尝试使用优先级最低的节点在java中创建优先级队列。但是，我的比较器不工作，输出非常奇怪。我相信我需要改变我的比较器，但我不知道如何改变它。这是我的代码：

public class HuffmanComparator implements Comparator<TreeNodeHuffman> {
    public int compare(TreeNodeHuffman p1, TreeNodeHuffman p2) {
        if (p1.frequency < p2.frequency) return -1;
        if (p1.frequency > p2.frequency) return 1;
        return 0;
    }    
}

public class TreeNodeHuffman {
public static void main(String[] args) {    
    HuffmanComparator compare = new HuffmanComparator();
    TreeNodeHuffman e = new TreeNodeHuffman('e', 12702);
    TreeNodeHuffman t = new TreeNodeHuffman('t', 9056);
    TreeNodeHuffman a = new TreeNodeHuffman('a', 8167);
    TreeNodeHuffman o = new TreeNodeHuffman('o', 7507);
    TreeNodeHuffman i = new TreeNodeHuffman('i', 6966);
    TreeNodeHuffman n = new TreeNodeHuffman('a', 6749);
    TreeNodeHuffman s = new TreeNodeHuffman('s', 6327);
    TreeNodeHuffman h = new TreeNodeHuffman('h', 6094);
    TreeNodeHuffman r = new TreeNodeHuffman('r', 5987);
    TreeNodeHuffman d = new TreeNodeHuffman('d', 4253);
    TreeNodeHuffman l = new TreeNodeHuffman('l', 4025);
    TreeNodeHuffman c = new TreeNodeHuffman('c', 2782);
    TreeNodeHuffman u = new TreeNodeHuffman('u', 2758);
    TreeNodeHuffman m = new TreeNodeHuffman('m', 2406);
    TreeNodeHuffman w = new TreeNodeHuffman('w', 2360);
    TreeNodeHuffman f = new TreeNodeHuffman('f', 2228);
    TreeNodeHuffman g = new TreeNodeHuffman('g', 2015);
    TreeNodeHuffman y = new TreeNodeHuffman('y', 1974);
    TreeNodeHuffman p = new TreeNodeHuffman('p', 1929);
    TreeNodeHuffman b = new TreeNodeHuffman('b', 1492);
    TreeNodeHuffman v = new TreeNodeHuffman('v', 978);
    TreeNodeHuffman k = new TreeNodeHuffman('k', 772);
    TreeNodeHuffman j = new TreeNodeHuffman('j', 153);
    TreeNodeHuffman x = new TreeNodeHuffman('x', 150);
    TreeNodeHuffman q = new TreeNodeHuffman('q', 95);
    TreeNodeHuffman z = new TreeNodeHuffman('z', 74);
    PriorityQueue<TreeNodeHuffman> queue = new PriorityQueue<TreeNodeHuffman>(26, compare);
    queue.add(e);
    queue.add(t);
    queue.add(a);
    queue.add(o);
    queue.add(i);
    queue.add(n);
    queue.add(s);
    queue.add(h);
    queue.add(r);
    queue.add(d);
    queue.add(l);
    queue.add(c);
    queue.add(u);
    queue.add(m);
    queue.add(w);
    queue.add(f);
    queue.add(g);
    queue.add(y);
    queue.add(p);
    queue.add(b);
    queue.add(v);
    queue.add(k);
    queue.add(j);
    queue.add(x);
    queue.add(q);
    queue.add(z);
    System.out.println(queue);
}
}

输出如下： [z，k，q，g，v，x，u，d，f，y，b，m，j，i，c，e，s，o，w，a，r，h，p，t，l ，一个]。但是，输出应该是[z，q，x，j，k，v，b ........]。提前谢谢！

Answer 1

您需要逐个轮询PriorityQueue中的项目。 toString不这样做。

所以代替你的System.out.println(queue);执行此操作：

while(!queue.isEmpty()) {
   System.out.println(queue.poll());
}

原因是PriorityQueue永远不会在内部完全排序，查找堆如何工作以获取更多细节。从中调查项目会在调用期间修复堆，因此它应该按排序顺序输出元素。

Answer 2

System.out.println(queue)正在打印未排序的队列。如果你想打印队列真实订单，请按照下面的代码使用poll来从队列的顶部到底部获取元素：

TreeNodeHuffman tn = null;
    do{
        tn = queue.poll();
        if(tn!=null){
            System.out.print(tn.key+",");
        }
    }while(tn != null);

您将按预期看到此输出：

Z，Q，X，J，K，V，B，P，Y，G，F，W，M，U，C，L，d，R，H，S，A，I，O，一，T，E，

Answer 3

您希望较低的频率更高：

  public int compare(TreeNodeHuffman p1, TreeNodeHuffman p2) {
          if (p1.frequency < p2.frequency) return 1;
          if (p1.frequency > p2.frequency) return -1;
          return 0;
      }    
   }

如果要测试它，请将其发送到单个线程池，并查看正在处理的作业的顺序，而不是字符串或迭代器。正如doc在http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html#iterator%28%29所说：

返回此队列中元素的迭代器。迭代器不会以任何特定顺序返回元素。

可以看到http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html#newSingleThreadExecutor%28%29用于快速单线程池来测试它。

Answer 4

@Thomas回答有效。

我的方法是产生相同的结果而不实际清空队列。因此，我改为在PriorityQueue上创建了包装器，并为其实现了next()和hasNext()。另外，要精确模拟优先级队列行为，请extend AbstractQueue和委托调用诸如offer，peek，poll和{{1} }通过PriorityQueue对象。

size

免责声明：这确实需要将整个队列复制到列表中并对其进行排序。

priorityQueueObject.methodName()

打印：

public class MyPriorityQueue<E extends Comparable<T>, T> extends AbstractQueue<E> {
    Integer arrOfInts[] = { 11, 7, 15, 10, 2, 1, 4, 5, 7, 2, 18, 1, 19};
    PriorityQueue<E> pq = new PriorityQueue<>();

    public static void main(String[] args) {
        MyPriorityQueue mpq = new MyPriorityQueue<>();
        mpq.addAll(Arrays.asList(arrOfInts));

        //Using iterator
        Iterator it = mpq.iterator();
        System.out.println("The internal priority queue:"  + mpq.pq);
        System.out.println("Using Iterator:");
        while(it.hasNext()) {
            System.out.print(it.next() + ", ");
        }

        System.out.println("\nUsing simple system out println:");
        System.out.println(mpq);

        System.out.println("Using foreach: ");
        for(Object o : mpq) {
            System.out.print(o + ", ");
        }
    }

    @Override
    public boolean offer(E arg0) {
        return pq.offer(arg0);
    }

    @Override
    public E peek() {
        return pq.peek();
    }

    @Override
    public E poll() {
        return pq.poll();
    }

    @Override
    public Iterator<E> iterator() {
        ArrayList<E> list = new ArrayList(Arrays.asList(pq.toArray()));
        Collections.sort(list, null);
        return new Iterator<E>() {
            @Override
            public boolean hasNext() {
                return !list.isEmpty();
            }

            @Override
            public E next() {
                assert (hasNext());
                return list.remove(0);
            }
        };
    }

    @Override
    public int size() {
        return pq.size();
    }
}

PriorityQueue.toString错误的元素顺序

4 个答案: