// Given a binary tree, find the largest Binary Search Tree (BST),
// where largest means BST with largest number of nodes in it.
// The largest BST must include all of its descendants.
public LargestBST largestBSTSubtree2(Node node)
{
if (node == null)
{
return(null);
}
if (node.Left == null && node.Right == null)
{
return(new LargestBST(node, node.GetHashCode(), node.Data, node.Data));
}
LargestBST LeftNode = largestBSTSubtree2(node.Left);
LargestBST RightNode = largestBSTSubtree2(node.Right);
if (LeftNode != null && RightNode != null)
{
if ((node.Data > LeftNode.max && node.Left == LeftNode.node) &&
(node.Data < RightNode.min && node.Right == RightNode.node))
{
LargestBST bst = new LargestBST(node,
LeftNode.maxNode + RightNode.maxNode + 1,
LeftNode.min,
RightNode.max);
return(bst);
}
else
{
return((LeftNode.maxNode > RightNode.maxNode) ? LeftNode : RightNode);
}
}
else if (LeftNode != null)
{
if (node.Data > LeftNode.max && node.Left == LeftNode.node)
{
return(new LargestBST(node, LeftNode.maxNode + 1, LeftNode.min, node.Data));
}
else
{
return(LeftNode);
}
}
else if (RightNode != null)
{
if (node.Data < RightNode.min && node.Right == RightNode.node)
{
return(new LargestBST(node, RightNode.maxNode + 1, node.Data, RightNode.max));
}
else
{
return(RightNode);
}
}
return(null);
}