Update 0538.把二叉搜索树转换为累加树.md

problems/0538.把二叉搜索树转换为累加树.md

@@ -200,8 +200,30 @@ class Solution {
 ```
 
 ## Python 
-**递归**
+递归法(版本一)
+```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 convertBST(self, root: TreeNode) -> TreeNode:
+        self.pre = 0  # 记录前一个节点的数值
+        self.traversal(root)
+        return root
+    def traversal(self, cur):
+        if cur is None:
+            return        
+        self.traversal(cur.right)
+        cur.val += self.pre
+        self.pre = cur.val
+        self.traversal(cur.left)
     
+        
+```
+递归法（版本二）
 ```python
 # Definition for a binary tree node.
 # class TreeNode:
@@ -234,7 +256,32 @@ class Solution:
         return root 
         
 ```
-**迭代**
+迭代法（版本一）
+```python
+class Solution:
+    def __init__(self):
+        self.pre = 0  # 记录前一个节点的数值
+    
+    def traversal(self, root):
+        stack = []
+        cur = root
+        while cur or stack:
+            if cur:
+                stack.append(cur)
+                cur = cur.right  # 右
+            else:
+                cur = stack.pop()  # 中
+                cur.val += self.pre
+                self.pre = cur.val
+                cur = cur.left  # 左
+    
+    def convertBST(self, root):
+        self.pre = 0
+        self.traversal(root)
+        return root
+
+```            
+迭代法（版本二）
 ```python
 class Solution:
     def convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]: