public void Delete(int key)
{
//first find the node in the tree to delete and assign to item pointer/reference
NodeForTree item = Find(key);
NodeForTree X = null;
NodeForTree Y = null;
if (item == null)
{
Console.WriteLine("Nothing to delete!");
return;
}
if (item.left == null || item.right == null)
{
Y = item;
}
else
{
Y = TreeSuccessor(item);
}
if (Y.left != null)
{
X = Y.left;
}
else
{
X = Y.right;
}
if (X != null)
{
X.parent = Y;
}
if (Y.parent == null)
{
root = X;
}
else if (Y == Y.parent.left)
{
Y.parent.left = X;
}
else
{
Y.parent.left = X;
}
if (Y != item)
{
item.Value = Y.Value;
}
if (Y.colour == RedOrBlack.Black)
{
DeleteFixUp(X);
}
}
private NodeForTree TreeSuccessor(NodeForTree X)
{
if (X.left != null)
{
return Minimum(X);
}
else
{
NodeForTree Y = X.parent;
while (Y != null && X == Y.right)
{
X = Y;
Y = Y.parent;
}
return Y;
}
}
private void RightRotate(NodeForTree Y)
{
// right rotate is simply mirror code from left rotate
NodeForTree X = Y.left;
Y.left = X.right;
if (X.right != null)
{
X.right.parent = Y;
}
if (X != null)
{
X.parent = Y.parent;
}
if (Y.parent == null)
{
root = X;
}
if (Y == Y.parent.right)
{
Y.parent.right = X;
}
if (Y == Y.parent.left)
{
Y.parent.left = X;
}
X.right = Y;//put Y on X's right
if (Y != null)
{
Y.parent = X;
}
}
private NodeForTree Minimum(NodeForTree X)
{
while (X.left.left != null)
{
X = X.left;
}
if (X.left.right != null)
{
X = X.left.right;
}
return X;
}
private void LeftRotate(NodeForTree X)
{
NodeForTree Y = X.right; // set Y
X.right = Y.left;//turn Y's left subtree into X's right subtree
if (Y.left != null)
{
Y.left.parent = X;
}
if (Y != null)
{
Y.parent = X.parent;//link X's parent to Y
}
if (X.parent == null)
{
root = Y;
}
if (X == X.parent.left)
{
X.parent.left = Y;
}
else
{
X.parent.right = Y;
}
Y.left = X; //put X on Y's left
if (X != null)
{
X.parent = Y;
}
}
private void InsertFixUp(NodeForTree item)
{
//Checks Red-Black Tree properties
while (item != root && item.parent.colour == RedOrBlack.Red)
{
/*We have a violation*/
if (item.parent == item.parent.parent.left)
{
NodeForTree Y = item.parent.parent.right;
if (Y != null && Y.colour == RedOrBlack.Red)//Case 1: uncle is red
{
item.parent.colour = RedOrBlack.Black;
Y.colour = RedOrBlack.Black;
item.parent.parent.colour = RedOrBlack.Red;
item = item.parent.parent;
}
else //Case 2: uncle is black
{
if (item == item.parent.right)
{
item = item.parent;
LeftRotate(item);
}
//Case 3: recolour & rotate
item.parent.colour = RedOrBlack.Black;
item.parent.parent.colour = RedOrBlack.Red;
RightRotate(item.parent.parent);
}
}
else
{
//mirror image of code above
NodeForTree X = null;
X = item.parent.parent.left;
if (X != null && X.colour == RedOrBlack.Black)//Case 1
{
item.parent.colour = RedOrBlack.Red;
X.colour = RedOrBlack.Red;
item.parent.parent.colour = RedOrBlack.Black;
item = item.parent.parent;
}
else //Case 2
{
if (item == item.parent.left)
{
item = item.parent;
RightRotate(item);
}
//Case 3: recolour & rotate
item.parent.colour = RedOrBlack.Black;
item.parent.parent.colour = RedOrBlack.Red;
LeftRotate(item.parent.parent);
}
}
root.colour = RedOrBlack.Black;//re-colour the root black as necessary
}
}
private void InOrderDisplay(NodeForTree current)
{
if (current != null)
{
InOrderDisplay(current.left);
Console.Write("({0}) ", current.Value);
InOrderDisplay(current.right);
}
}
private void DeleteFixUp(NodeForTree X)
{
while (X != null && X != root && X.colour == RedOrBlack.Black)
{
if (X == X.parent.left)
{
NodeForTree W = X.parent.right;
if (W.colour == RedOrBlack.Red)
{
W.colour = RedOrBlack.Black; //case 1
X.parent.colour = RedOrBlack.Red; //case 1
LeftRotate(X.parent); //case 1
W = X.parent.right; //case 1
}
if (W.left.colour == RedOrBlack.Black && W.right.colour == RedOrBlack.Black)
{
W.colour = RedOrBlack.Red; //case 2
X = X.parent; //case 2
}
else if (W.right.colour == RedOrBlack.Black)
{
W.left.colour = RedOrBlack.Black; //case 3
W.colour = RedOrBlack.Red; //case 3
RightRotate(W); //case 3
W = X.parent.right; //case 3
}
W.colour = X.parent.colour; //case 4
X.parent.colour = RedOrBlack.Black; //case 4
W.right.colour = RedOrBlack.Black; //case 4
LeftRotate(X.parent); //case 4
X = root; //case 4
}
else //mirror code from above with "right" & "left" exchanged
{
NodeForTree W = X.parent.left;
if (W.colour == RedOrBlack.Red)
{
W.colour = RedOrBlack.Black;
X.parent.colour = RedOrBlack.Red;
RightRotate(X.parent);
W = X.parent.left;
}
if (W.right.colour == RedOrBlack.Black && W.left.colour == RedOrBlack.Black)
{
W.colour = RedOrBlack.Black;
X = X.parent;
}
else if (W.left.colour == RedOrBlack.Black)
{
W.right.colour = RedOrBlack.Black;
W.colour = RedOrBlack.Red;
LeftRotate(W);
W = X.parent.left;
}
W.colour = X.parent.colour;
X.parent.colour = RedOrBlack.Black;
W.left.colour = RedOrBlack.Black;
RightRotate(X.parent);
X = root;
}
}
if (X != null)
X.colour = RedOrBlack.Black;
}
public void Insert(int item)
{
NodeForTree newItem = new NodeForTree(item);
if (root == null)
{
root = newItem;
root.colour = RedOrBlack.Black;
return;
}
NodeForTree Y = null;
NodeForTree X = root;
while (X != null)
{
Y = X;
if (newItem.Value < X.Value)
{
X = X.left;
}
else
{
X = X.right;
}
}
newItem.parent = Y;
if (Y == null)
{
root = newItem;
}
else if (newItem.Value < Y.Value)
{
Y.left = newItem;
}
else
{
Y.right = newItem;
}
newItem.left = null;
newItem.right = null;
newItem.colour = RedOrBlack.Red;//colour the new node red
InsertFixUp(newItem);//call method to check for violations and fix
}
