/// <summary>Removes the entry at the top of the heap.</summary>
/// <returns>The removed entry.</returns>
public virtual object Remove()
{
// Get the first item and save it for later (this is what will be returned).
if (_list.Count == 0)
{
throw new InvalidOperationException("Cannot remove an item from the heap as it is empty.");
}
object toReturn = ((ChoBinaryHeapEntry)_list[0]).Value;
// Remove the first item
_list.RemoveAt(0);
// See if we can stop now (if there's only one item or we're empty, we're done)
if (_list.Count > 1)
{
// Move the last element to the beginning
_list.Insert(0, _list[_list.Count - 1]);
_list.RemoveAt(_list.Count - 1);
// Start reheapify
int current = 0, possibleSwap = 0;
// Keep going until the tree is a heap
while (true)
{
// Get the positions of the node's children
int leftChildPos = 2 * current + 1;
int rightChildPos = leftChildPos + 1;
// Should we swap with the left child?
if (leftChildPos < _list.Count)
{
// Get the two entries to compare (node and its left child)
ChoBinaryHeapEntry entry1 = (ChoBinaryHeapEntry)_list[current];
ChoBinaryHeapEntry entry2 = (ChoBinaryHeapEntry)_list[leftChildPos];
// If the child has a higher key than the parent, set that as a possible swap
if (entry2.CompareTo(entry1) > 0)
{
possibleSwap = leftChildPos;
}
}
else
{
break; // if can't swap this, we're done
}
// Should we swap with the right child? Note that now we check with the possible swap
// position (which might be current and might be left child).
if (rightChildPos < _list.Count)
{
// Get the two entries to compare (node and its left child)
ChoBinaryHeapEntry entry1 = (ChoBinaryHeapEntry)_list[possibleSwap];
ChoBinaryHeapEntry entry2 = (ChoBinaryHeapEntry)_list[rightChildPos];
// If the child has a higher key than the parent, set that as a possible swap
if (entry2.CompareTo(entry1) > 0)
{
possibleSwap = rightChildPos;
}
}
// Now swap current and possible swap if necessary
if (current != possibleSwap)
{
object temp = _list[current];
_list[current] = _list[possibleSwap];
_list[possibleSwap] = temp;
}
else
{
break; // if nothing to swap, we're done
}
// Update current to the location of the swap
current = possibleSwap;
}
}
// Return the item from the heap
return(toReturn);
}
