Merge pull request #2553 from raydemo1/master

Update 0102.二叉树的层序遍历.md Python层序遍历递归法更简洁

problems/0102.二叉树的层序遍历.md

@@ -210,18 +210,24 @@ class Solution:
 #         self.right = right
 class Solution:
     def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
-        levels = []
-        self.helper(root, 0, levels)
-        return levels
+        if not root:
+            return []
 
-    def helper(self, node, level, levels):
+        levels = []
+
+        def traverse(node, level):
             if not node:
                 return
+
             if len(levels) == level:
                 levels.append([])
+
             levels[level].append(node.val)
-        self.helper(node.left, level + 1, levels)
-        self.helper(node.right, level + 1, levels)
+            traverse(node.left, level + 1)
+            traverse(node.right, level + 1)
+
+        traverse(root, 0)
+        return levels
 
 ```