Merge pull request #225 from jojoo15/patch-19

添加 0538.把二叉搜索树转换为累加树 python3版本

problems/0538.把二叉搜索树转换为累加树.md

@@ -196,8 +196,26 @@ class Solution {
 ```
 
 Python：
-
+```python3
-
+# 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
+#递归法
+class Solution:
+    def convertBST(self, root: TreeNode) -> TreeNode:
+        def buildalist(root): 
+            if not root: return None
+            buildalist(root.right)  #右中左遍历
+            root.val += self.pre
+            self.pre = root.val
+            buildalist(root.left)
+        self.pre = 0  #记录前一个节点的数值
+        buildalist(root)
+        return root
+```
 Go：
 
 
@@ -207,4 +225,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>