public boolean hasNext() {
return !copy.isEmpty();
}
public Integer next() {
if (!hasNext()) throw new NoSuchElementException();
return copy.delMin();
}
// add all elements to copy of heap
// takes linear time since already in heap order so no keys move
public HeapIterator() {
copy = new IndexMinPQ<Key>(pq.length - 1);
for (int i = 1; i <= N; i++) copy.insert(pq[i], keys[pq[i]]);
}