添加leetcode 226翻转二叉树python后序递归代码

problems/0226.翻转二叉树.md

@@ -322,6 +322,18 @@ class Solution:
         return root
 ```
 
+递归法：后序遍历：
+```python
+class Solution:
+    def invertTree(self, root: TreeNode) -> TreeNode:
+        if root is None:
+            return None
+        self.invertTree(root.left)
+        self.invertTree(root.right)
+        root.left, root.right = root.right, root.left
+        return root 
+```
+
 迭代法：深度优先遍历（前序遍历）：
 ```python
 class Solution: