Why is My PriorityQueue\'s toString Output Disordered Despite a Correct Comparator?

PriorityQueue Order Discrepancy in toString Output

The issue stems from the incorrect usage of PriorityQueue's toString method when the comparator doesn't sort the elements as expected.

Comparator Error

In the given comparator HuffmanComparator, the code should be modified as follows to prioritize nodes with lower frequency:

<code class="java">public int compare(TreeNodeHuffman p1, TreeNodeHuffman p2) {
  if (p1.frequency > p2.frequency) return -1;
  if (p1.frequency < p2.frequency) return 1;
  return 0;
}</code>

toString and Polling

Although the comparator is now correct, PriorityQueue's toString method does not guarantee the elements are fully sorted. To obtain the sorted elements, we should poll the items one by one using a while loop:

<code class="java">while (!queue.isEmpty()) {
  System.out.println(queue.poll());
}</code>

This approach ensures the heap structure is fixed during each call to poll, resulting in the desired order of elements in the output.

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