fixed balanced bst

Author: mihirs16

14. Questions/leetcode 110 - balanced bst.py

@@ -10,7 +10,7 @@ def __init__(self, val=0, left=None, right=None):
         self.right = right
 
 class Solution:
-    def isBalanced(self, root: Optional[TreeNode]) -> bool:
+    def isBalanced(self, root) -> bool:
         def dfs(root):
             if root is None: return [True, 0]