Find the rank w.r.t K - Number of nodes with value less than K

If the rank of the BST is k, it implies how many nodes/keys are less than k.

So, it boils down to 3 easy recursive calls

• In the simplest case if K==node value, then whole of the let is rank of the node
• if K < node.value then we know that rank depends on the size of left sub tree and its less than sub tree's length
• If K > node.value then we know that we have to count full left subtree w.r.t with that node, and some nodes in right

public int rank(int K, node x)
{
   if(x==null) return 0;
   if(K < x.data)   return rank(K,x.left);
   else if(K > x.data)   return 1 + size(x.left) + rank(K,x.right);
   else if(K == x.data)   return size(x.left);   
}