CareerCup

private static boolean isBST(BSTNode root) {
		if (root == null)
			return true;

		if (root.getLeft() != null && findMax(root.getLeft()) > root.getData())
			return false;
		if (root.getRight() != null
				&& findMin(root.getRight()) < root.getData())
			return false;

		if (!(isBST(root.getLeft())) || (!isBST(root.getRight())))
			return false;
		return true;
	}

If the inorder traversal of a binary tree is in sorted order then the tree is a binary tree.

C++ Version:

int isBST(struct node* node) { 
  return(checkIsBST(node, INT_MIN, INT_MAX)); 
}

int checkIsBST(struct node* node, int min, int max) { 
  if (node==NULL) 
	return true;

  if (node->data<min || node->data>max) 
	return false;

  return 
     ( checkIsBST(node->left, min, node->data) && 
       checkIsBST(node->right, node->data+1, max) ); 
}