java - 为什么 PriorityQueue.toString 返回错误的元素顺序？

Question

这个问题已经有答案了:

The built-in iterator for java's PriorityQueue does not traverse the data structure in any particular order. Why? (5 个回答)

已关闭 1 年前。

我正在尝试在java中创建一个优先级队列，其中优先级频率最低的节点。然而，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);
}
}

输出结果如下:[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........]。

Answer 1

您需要逐一轮询PriorityQueue中的项目。 toString 不会这样做。

因此，不要使用 System.out.println(queue); 这样做:

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

原因是 PriorityQueue 内部永远不会完全排序，请查看堆的工作原理以了解更多详细信息。从中轮询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。