Update 二叉树的递归遍历.md

problems/二叉树的递归遍历.md

@@ -174,50 +174,45 @@ class Solution {
 Python：
 ```python
 # 前序遍历-递归-LC144_二叉树的前序遍历
+# 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 preorderTraversal(self, root: TreeNode) -> List[int]:
-        # 保存结果
+        if not root:
-        result = []
+            return []
 
-        def traversal(root: TreeNode):
+        left = self.preorderTraversal(root.left)
-            if root == None:
+        right = self.preorderTraversal(root.right)
-                return
+
-            result.append(root.val) # 前序
+        return  [root.val] + left +  right
-            traversal(root.left)    # 左
-            traversal(root.right)   # 右
 
-        traversal(root)
-        return result
 
 # 中序遍历-递归-LC94_二叉树的中序遍历
 class Solution:
     def inorderTraversal(self, root: TreeNode) -> List[int]:
-        result = []
+        if root is None:
+            return []
 
-        def traversal(root: TreeNode):
+        left = self.inorderTraversal(root.left)
-            if root == None:
+        right = self.inorderTraversal(root.right)
-                return
-            traversal(root.left)    # 左
-            result.append(root.val) # 中序
-            traversal(root.right)   # 右
 
-        traversal(root)
+        return left + [root.val] + right
-        return result
 
 # 后序遍历-递归-LC145_二叉树的后序遍历
 class Solution:
     def postorderTraversal(self, root: TreeNode) -> List[int]:
-        result = []
+        if not root:
+            return []
 
-        def traversal(root: TreeNode):
+        left = self.postorderTraversal(root.left)
-            if root == None:
+        right = self.postorderTraversal(root.right)
-                return
-            traversal(root.left)    # 左
-            traversal(root.right)   # 右
-            result.append(root.val) # 后序
 
-        traversal(root)
+        return left + right + [root.val]
-        return result
 ```
 
 Go：