// Grows child 'i' to make sure it's possible to remove an
// item from it while keeping it at minItems, then calls remove to actually
// remove it
//
// Most documentation says we have to do two sets of special casing:
// 1) item is in this node
// 2) item is in child
// In both cases, we need to handle the two subcases:
// A) node has enough values that it can spare one
// B) node doesn't have enough values
// For the latter, we have to check:
// a) left sibling has node to spare
// b) right sibling has node to spare
// c) we must merge
// To simplify our code here, we handle cases #1 and #2 the same:
// If a node doesn't have enough items, we make sure it does (using a,b,c).
// We then simply redo our remove call, and the second time (regardless of
// whether we're in case 1 or 2), we'll have enough items and can guarantee
// that we hit case A.
public T GrowChildAndRemove(int i, T item, int minItems, ToRemove typ)
{
if (i > 0 && Children[i - 1].Items.Length > minItems)
{
// Steal from left child
Node <T> child = MutableChild(i);
Node <T> stealFrom = MutableChild(i - 1);
T stolenItem = stealFrom.Items.Pop();
child.Items.InsertAt(0, Items[i - 1]);
Items[i - 1] = stolenItem;
if (stealFrom.Children.Length > 0)
{
child.Children.InsertAt(0, stealFrom.Children.Pop());
}
}
else if (i < Items.Length && Children[i + 1].Items.Length > minItems)
{
// steal from right child
Node <T> child = MutableChild(i);
Node <T> stealFrom = MutableChild(i + 1);
T stolenItem = stealFrom.Items.RemoveAt(0);
child.Items.Append(Items[i]);
Items[i] = stolenItem;
if (stealFrom.Children.Length > 0)
{
child.Children.Append(stealFrom.Children.RemoveAt(0));
}
}
else
{
if (i >= Items.Length)
{
i--;
}
Node <T> child = MutableChild(i);
// merge with right child
T mergeItem = Items.RemoveAt(i);
Node <T> mergeChild = Children.RemoveAt(i + 1);
child.Items.Append(mergeItem);
child.Items.Append(mergeChild.Items);
child.Children.Append(mergeChild.Children);
_ = Cow.FreeNode(mergeChild);
}
return(Remove(item, minItems, typ));
}