delete_node_in_a_BST.py

class Solution(object):
    def deleteNode(self, root, key):
        if not root:
            return root
        if key < root.val:
            root.left = self.deleteNode(root.left, key)
        elif key > root.val:
            root.right = self.deleteNode(root.right, key)
        else:
            if not root.left:
                return root.right
            elif not root.right:
                return root.left
            successor = root.right
            while successor.left:
                successor = successor.left
            root.val = successor.val
            root.right = self.deleteNode(root.right, successor.val)
        return root