Update 0110.平衡二叉树.md python code via iterate

In the original method, we need to traversal every node and write the function named getDepth to get the depth of all sub trees in traverse method too.
But there is more suitable uniform iteration traversal algorithm, I use the map struct in the code segment where the node is Null.
If you have problem in understand, please feel free to communicate with me.

problems/0110.平衡二叉树.md

@@ -531,40 +531,26 @@ class Solution:
 迭代法：
 ```python
 class Solution:
-    def isBalanced(self, root: TreeNode) -> bool:
+    def isBalanced(self, root: Optional[TreeNode]) -> bool:
-        st = []
         if not root:
             return True
-        st.append(root)
+
-        while st:
+        height_map = {}
-            node = st.pop() #中
+        stack = [root]
-            if abs(self.getDepth(node.left) - self.getDepth(node.right)) > 1:
+        while stack:
-                return False
+            node = stack.pop()
-            if node.right:
-                st.append(node.right) #右（空节点不入栈）
-            if node.left:
-                st.append(node.left) #左（空节点不入栈）
-        return True
-    
-    def getDepth(self, cur):
-        st = []
-        if cur:
-            st.append(cur)
-        depth = 0
-        result = 0
-        while st:
-            node = st.pop()
             if node:
-                st.append(node) #中
+                stack.append(node)
-                st.append(None)
+                stack.append(None)
-                depth += 1
+                if node.left: stack.append(node.left)
-                if node.right: st.append(node.right) #右
+                if node.right: stack.append(node.right)
-                if node.left: st.append(node.left) #左
             else:
-                node = st.pop()
+                real_node = stack.pop()
-                depth -= 1
+                left, right = height_map.get(real_node.left, 0), height_map.get(real_node.right, 0)
-            result = max(result, depth)
+                if abs(left - right) > 1:
-        return result
+                    return False
+                height_map[real_node] = 1 + max(left, right)
+        return True
 ```