peek

Returns the highest-priority (smallest) element without removing it. Returns null if the queue is empty.

Example:

    var pq = new PriorityQueue<string> ((a, b) => {
        return strcmp (a, b);
    });
    pq.add ("b");
    pq.add ("a");
    assert (pq.peek () == "a");
    assert (pq.size () == 2);

Returns:

the smallest element, or null if empty.