PriorityQueue, what am I missing?

Question

I have a comparator class NComparator that compares 2 Node objects and returns either 1, -1, or 0.

I initialized a PriorityQueue with an initial capacity of 100 and that NComparator.

    NComparator nc = new NComparator();
    PriorityQueue<Node> pq = new PriorityQueue<Node>(100, nc);

I have about 25 Node objects (that can be compared with NComparator), and I added them all to the PriorityQueue Object:

  pq.add(new Node("A", 3));
  pq.add(new Node("G", 1));
  pq.add(new Node("B", 10));
  .... etc

How can I arrange these node objects in PriorityQueue by the priority returned by the comparator (which only compares pairwise combinations of nodes)? Specifically, I would like to be able to access the two nodes with the least priority in this PriorityQueue. How can I do that?

This will help http://stackoverflow.com/questions/11003155/change-priorityqueue-to-max-priorityqueue — Mehul Rathod, Jul 09 '13 at 21:39

score 2 · Accepted Answer · answered Jul 09 '13 at 21:42

2

The PriorityQueue API only supports getting the single node with the least priority, but you could remove that and then query again to get the next lowest element.

answered Jul 09 '13 at 21:42

Louis Wasserman

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Thanks, I see. I did not also realize that when I do pq.add, PriorityQueue automatically adds them so they are always retained in order. So removing on element will be removing its lowest priority. – Jul 09 '13 at 22:24

score 0 · Answer 2 · answered Jul 09 '13 at 22:10

If are you sure that your NComparator arranges the Node elements correctly, and the least priorities are at the head of the queue, then you only need to do, twice: pq.poll() See the PriorityQueue API

Example:

  Node firstLowerNode = pq.poll();
  Node secondLowerNode = pq.poll();

PriorityQueue, what am I missing?

2 Answers2