public bool IsValidBST(BNode root)
{
return(Helper(root, int.MinValue, int.MaxValue));
}
public BNode DeleteNode(BNode root, int key)
{
BNode curr = root;
BNode prev = null;
BNode child = null;
BNode succ = null;
while (curr != null)
{
if (curr.data == key)
{
break;
}
else if (key < curr.data)
{
prev = curr;
curr = curr.left;
}
else
{
prev = curr;
curr = curr.right;
}
}
//Key not found
if (curr == null)
{
return(root);
}
// If the deleted node is leaf node
if (curr.left == null && curr.right == null)
{
if (prev == null)
{
return(null);
}
if (curr == prev.left)
{
prev.left = null;
}
else
{
prev.right = null;
}
}
// If the deleted node has both right and left subtrees
// Find successor of the key and copy it to the curr
else if (curr.left != null && curr.right != null)
{
prev = curr;
succ = curr.right;
while (succ.left != null)
{
prev = succ;
succ = succ.left;
}
curr.data = succ.data;
if (prev.right == succ)
{
prev.right = succ.right;
}
else
{
prev.left = succ.right;
}
}
// If the deleted node has only either right or left subtree
else if (curr.left != null || curr.right != null)
{
if (curr.right != null)
{
child = curr.right;
}
if (curr.left != null)
{
child = curr.left;
}
// if root node itself is deleted
if (prev == null)
{
root = child;
return(root);
}
if (curr == prev.left)
{
prev.left = child;
}
else
{
prev.right = child;
}
}
return(root);
}