diff --git a/problems/0404.左叶子之和.md b/problems/0404.左叶子之和.md
index e55981e2..ffcd2c8c 100644
--- a/problems/0404.左叶子之和.md
+++ b/problems/0404.左叶子之和.md
@@ -171,10 +171,10 @@ class Solution {
         int rightValue = sumOfLeftLeaves(root.right);  // 右
                                                        
         int midValue = 0;
-        if (root.left != null && root.left.left == null && root.left.right == null) { // 中
+        if (root.left != null && root.left.left == null && root.left.right == null) { 
             midValue = root.left.val;
         }
-        int sum = midValue + leftValue + rightValue;
+        int sum = midValue + leftValue + rightValue;  // 中
         return sum;
     }
 }
@@ -230,8 +230,8 @@ class Solution {
 
 ## Python 
 
-**递归**
-```python
+**递归后序遍历**
+```python3
 class Solution:
     def sumOfLeftLeaves(self, root: TreeNode) -> int:
         if not root: 
@@ -242,13 +242,13 @@ class Solution:
         
         cur_left_leaf_val = 0
         if root.left and not root.left.left and not root.left.right: 
-            cur_left_leaf_val = root.left.val  # 中
+            cur_left_leaf_val = root.left.val 
             
-        return cur_left_leaf_val + left_left_leaves_sum + right_left_leaves_sum
+        return cur_left_leaf_val + left_left_leaves_sum + right_left_leaves_sum # 中
 ```
 
 **迭代**
-```python
+```python3
 class Solution:
     def sumOfLeftLeaves(self, root: TreeNode) -> int:
         """