Inorder successor in a binary search tree

Question

This is a common algorithm question. I'm trying to find the inorder successor in a binary search tree. Here's my code

def inorderSuccessor(self, root, p):
        """
        :type root: TreeNode
        :type p: TreeNode
        :rtype: TreeNode
        """
        # if Node has a right child, go all the way down
        if p.right:
            curr = p
            while curr.left:
                curr = curr.left
            return curr
        # first ancestor whose left child the node is
        ans = None
        curr = root
        while curr is not p:
            if curr.val < p.val:
                curr = curr.right
            else:
                ans = curr
                curr = curr.left
        return ans

The problem is that this doesn't work when p is the highest node in the tree. I've been scratching my head over how to get this edge case going.

Answer 1

You can implement a method within your BST Class as below

def InOrderSucc(self,childNode):
    if(self.search(childNode)):
        if not (self.data == childNode):
            return(self.right.InOrderSucc(childNode))
        else:
            if(self.right):
                return(self.right.data)
            else:
                return None
    else:
        return False

where childNode is the Node you are requesting to find its InOrder Successor, Noting that the InOrder Successor will always be the right Child.