title: Finding the largest subtree in a BST
body: <p>Given a binary tree, I want to find out the largest subtree which is a BST in it.</p>
  
  <p>Naive approach:</p>
  
  <p>I have a naive approach in mind where I visit every node of the tree and pass this node to a isBST function. I will also keep track of the number of nodes in a sub-tree if it is a BST.</p>
  
  <p>Is there a better approach than this ? </p>