Update 0404.左叶子之和.md

problems/0404.左叶子之和.md

@@ -250,19 +250,27 @@ class Solution {
 
 **递归后序遍历**
 ```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
 class Solution:
-    def sumOfLeftLeaves(self, root: TreeNode) -> int:
+    def sumOfLeftLeaves(self, root: Optional[TreeNode]) -> int:
         if not root:
             return 0
         
-        left_left_leaves_sum = self.sumOfLeftLeaves(root.left)  # 左
-        right_left_leaves_sum = self.sumOfLeftLeaves(root.right) # 右
-        
-        cur_left_leaf_val = 0
+        # 检查根节点的左子节点是否为叶节点
         if root.left and not root.left.left and not root.left.right:
-            cur_left_leaf_val = root.left.val 
+            left_val = root.left.val
+        else:
+            left_val = self.sumOfLeftLeaves(root.left)
             
-        return cur_left_leaf_val + left_left_leaves_sum + right_left_leaves_sum # 中
+        # 递归地计算右子树左叶节点的和
+        right_val = self.sumOfLeftLeaves(root.right)
+        
+        return left_val + right_val
 ```
 
 **迭代**