public PriorityQueueItem<T> Dequeue()
{
// assumes pq is not empty; up to calling code
int li = data.Count - 1; // last index (before removal)
PriorityQueueItem<T> frontItem = data[0]; // fetch the front
data[0] = data[li];
data.RemoveAt(li);
--li; // last index (after removal)
int pi = 0; // parent index. start at front of pq
while (true)
{
int ci = pi * 2 + 1; // left child index of parent
if (ci > li)
{
break; // no children so done
}
int rc = ci + 1; // right child
if (rc <= li && data[rc].Priority - data[ci].Priority < 0)
{
// if there is a rc (ci + 1), and it is smaller than left child, use the rc instead
ci = rc;
}
if (data[pi].Priority - data[ci].Priority <= 0)
{
break; // parent is smaller than (or equal to) smallest child so done
}
PriorityQueueItem<T> tmp = data[pi];// swap parent and child
data[pi] = data[ci];
data[ci] = tmp;
pi = ci;
}
return frontItem;
}
public void Enqueue(PriorityQueueItem<T> item)
{
data.Add(item);
int ci = data.Count - 1; // child index; start at end
while (ci > 0)
{
int pi = (ci - 1) / 2; // parent index
if (data[ci].Priority - data[pi].Priority >= 0)
{
break; // child item is larger than (or equal) parent so we're done
}
PriorityQueueItem<T> tmp = data[ci];
data[ci] = data[pi];
data[pi] = tmp;
ci = pi;
}
}
public PriorityQueueItem<T> Peek()
{
PriorityQueueItem<T> frontItem = data[0];
return frontItem;
}