private void sink(int k) {
while (2 * k <= N) {
int j = 2 * k;
if (j < N && greater(j, j + 1)) j++;
if (!greater(k, j)) break;
exch(k, j);
k = j;
}
}
/**
* Removes and returns a smallest key on the priority queue.
*
* @return a smallest key on the priority queue
* @throws java.util.NoSuchElementException if the priority queue is empty
*/
public Key delMin() {
if (isEmpty()) throw new NoSuchElementException("Priority queue underflow");
exch(1, N);
Key min = pq[N--];
sink(1);
pq[N + 1] = null; // avoid loitering and help with garbage collection
if ((N > 0) && (N == (pq.length - 1) / 4)) resize(pq.length / 2);
assert isMinHeap();
return min;
}
/**
* ********************************************************************* Helper functions to
* restore the heap invariant.
* ********************************************************************
*/
private void swim(int k) {
while (k > 1 && greater(k / 2, k)) {
exch(k, k / 2);
k = k / 2;
}
}