/// <summary>
/// Tries moving to next entry by ascending order.
/// </summary>
bool Ascend()
{
curIndex++;
if (curNode.IsLeaf)
{
while (true)
{
// If a valid entry in node was found, return it.
if (curIndex < curNode.EntryCount)
{
curEntry = curNode.GetEntry(curIndex);
return(true);
}
// Else if no valid entry in node and there is a parent node
else if (curNode.ParentId != 0)
{
// Adjust index to point to current node in parent.
curIndex = curNode.IndexInParent();
// Set target node one level up.
curNode = nodeManager.Find(curNode.ParentId);
// Validate parent
if (curIndex < 0 || curNode == null)
{
throw new Exception("An error in BTree was detected.");
}
}
// No more parent nodes and valid entries. We should just finish off here
else
{
curEntry = null;
isFinished = true;
return(false);
}
}
}
else
{
do
{
// Get the next child node on first iteration,
// or the first child node on further iterations.
curNode = curNode.GetChildNode(curIndex);
// Reset index to 0 to indicate first child and entry in the newly found node.
curIndex = 0;
// Validate new node
if (curNode == null)
{
throw new Exception("An error in BTree was detected.");
}
}while(!curNode.IsLeaf);
curEntry = curNode.GetEntry(curIndex);
return(true);
}
}
bool MoveForward()
{
// Leaf node, either move right or up
if (currentNode.IsLeaf)
{
// First, move right
currentEntry++;
while (true)
{
// If currentEntry is valid
// then we are done here.
if (currentEntry < currentNode.EntriesCount)
{
current = currentNode.GetEntry(currentEntry);
return(true);
}
// If can't move right then move up
else if (currentNode.ParentId != 0)
{
currentEntry = currentNode.IndexInParent();
currentNode = nodeManager.Find(currentNode.ParentId);
// Validate move up result
if ((currentEntry < 0) || (currentNode == null))
{
throw new Exception("Something gone wrong with the BTree");
}
}
// If can't move up when we are done iterating
else
{
current = null;
doneIterating = true;
return(false);
}
}
}
// Parent node, always move right down
else
{
currentEntry++; // Increase currentEntry, this make firstCall to nodeManager.Find
// to return the right node, but does not affect subsequence calls
do
{
currentNode = currentNode.GetChildNode(currentEntry);
currentEntry = 0;
} while (false == currentNode.IsLeaf);
current = currentNode.GetEntry(currentEntry);
return(true);
}
}
/// <summary>
/// Splits this node to left and right nodes.
/// </summary>
public void Split(out TreeNode <K, V> leftNode, out TreeNode <K, V> rightNode)
{
Debug.Assert(IsOverflow, "This node is not yet overflowing.");
bool isLeaf = IsLeaf;
var halfCount = nodeManager.MinEntriesPerNode;
var middleEntry = entries[halfCount];
// Get larger entries and children for new node.
var largeEntries = new Tuple <K, V> [halfCount];
uint[] largeChildren = null;
// Copy larger entries to newer node.
entries.CopyTo(halfCount + 1, largeEntries, 0, halfCount);
// Copy child node ids if not a leaf.
if (!isLeaf)
{
largeChildren = new uint[halfCount + 1];
childrenIds.CopyTo(halfCount + 1, largeChildren, 0, halfCount);
}
// Create larger node
var largeNode = nodeManager.Create(largeEntries, largeChildren);
// All child nodes moved to newer node must refresh their parentId.
if (!isLeaf)
{
for (int i = 0; i < largeChildren.Length; i++)
{
nodeManager.Find(largeChildren[i]).ParentId = largeNode.id;
}
}
// Remove all large entries and children ids from this node.
// Entries list must also remove the middle entry because it will go to the parent node.
entries.RemoveRange(halfCount);
if (!isLeaf)
{
childrenIds.RemoveRange(halfCount + 1);
}
// Try getting parent node
var parentNode = parentId == 0 ? null : nodeManager.Find(parentId);
// If no parent, create a new parent node with the middle entry
if (parentNode == null)
{
parentNode = nodeManager.CreateNewRoot(
middleEntry.Item1,
middleEntry.Item2,
id,
largeNode.id
);
// Reassign parent id
this.ParentId = parentNode.id;
largeNode.ParentId = parentNode.id;
}
// Move the middle element to the parent node.
else
{
int insertIndex = 0;
parentNode.InsertAsParent(
middleEntry.Item1,
middleEntry.Item2,
id,
largeNode.id,
out insertIndex
);
// Reassign parent id for large node only because this node's already been set.
largeNode.ParentId = parentNode.id;
// Split parent node if overflowing.
if (parentNode.IsOverflow)
{
Split();
}
}
// Output nodes
leftNode = this;
rightNode = largeNode;
// Mark this node dirty
nodeManager.MarkAsChanged(this);
}
//
// Public Methods
//
/// <summary>
/// Remove an entry from this instance.
/// </summary>
public void Remove(int removeAt)
{
// Validate argument
if (false == (removeAt >= 0) && (removeAt < this.entries.Count))
{
throw new ArgumentOutOfRangeException();
}
// http://webdocs.cs.ualberta.ca/~holte/T26/del-b-tree.html
// https://en.wikipedia.org/wiki/B-tree#Deletion
// If this is a node leave, flagged entry will be removed
if (IsLeaf)
{
// Step 1: Remove X from the current node.
// Being a leaf node there are no subtrees to worry about.
entries.RemoveAt(removeAt);
nodeManager.MarkAsChanged(this);
// If the removal does not cause underflow then we are done here
if ((EntriesCount >= nodeManager.MinEntriesPerNode) || (parentId == 0))
{
return;
}
// Otherwise, rebalance this node
else
{
Rebalance();
}
}
// If the value to be deleted does not occur in a leaf,
// we replace it with the largest value in its left subtree
// and then proceed to delete that value from the node that
// originally contained it
else
{
// Grab the largest entry on the left subtree
var leftSubTree = nodeManager.Find(this.childrenIds[removeAt]);
TreeNode <K, V> largestNode; int largestIndex;
leftSubTree.FindLargest(out largestNode, out largestIndex);
var replacementEntry = largestNode.GetEntry(largestIndex);
// REplace it
this.entries[removeAt] = replacementEntry;
nodeManager.MarkAsChanged(this);
// Remove it from the node we took it from
largestNode.Remove(largestIndex);
}
}
