CareerCup

/* check for BST */
	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;
	}

/* Check for binary tree whether its binary search tree */
	private static boolean isBST(BSTNode root, int prev) {
		if(root==null)
			return true;
		if(!isBST(root.getLeft(),prev))
			return false;
		if(root.getData()<prev)
			return false;
		prev=root.getData();
		
		return isBST(root.getRight(),prev);
	}

bool IsBst(Node n) {
 if (n == null) return true;

 if (n.left != null && n.right != null) {
  if (n.val < n.left.val || n.val > n.right.val) return false;
 } else {
  if (n.left != null) {
   if (n.val < n.left.val) return false;
  } else {
     if (n.right != null) {
      if (n.val > n.right.val) return false;
     } else 
        return true;
  }
 }
 return IsBst(n.left) && IsBst(n.right);
}

O(n) - time & space (use of stack)

Already discussed id=8186287

bool isBST(Node * ptr)
{
	if (ptr==NULL) return TRUE;
	if (ptr->right == NULL && isBST(ptr->left) && ptr->value > ptr->left->value )return TRUE;
	if (ptr->left == NULL && isBST(ptr->right) && ptr->value < ptr->left->value )return TRUE;
	if(isBST(ptr->left)&& isBST(ptr->right) && ptr->value > ptr->left->value &&  ptr->value < ptr->left->value) return TRUE;
	return FALSE;

}

bool isBST(Node * ptr)
{
	if (ptr==NULL) return TRUE;
	if (ptr->right == NULL && isBST(ptr->left) && ptr->value > ptr->left->value )return TRUE;
	if (ptr->left == NULL && isBST(ptr->right) && ptr->value < ptr->right->value )return TRUE;
	if(isBST(ptr->left)&& isBST(ptr->right) && ptr->value > ptr->left->value &&  ptr->value < ptr->left->value) return TRUE;
	return FALSE;

}

Roy that solution does not work. See the above post by "Anonymous" (it was me). It will fail that tree.

please visit this site : code-forum.blogspot.com/2010/12/is-bst-or-not.html

bool isValidBST(node *p, int minAllowedValue, int maxAllowedValue)
{
if(p == null)
return true;

if(p->value < minAllowedValue || p->value > maxAllowedValue)
return false;

return isValidBST(p->left, minAllowedValue, p->value)
&& isValidBST(p->right, p->value, maxAllowedValue);

}