Merge pull request #181 from jojoo15/patch-11

添加 0098.验证二叉搜索树 python版本

problems/0098.验证二叉搜索树.md

@@ -336,8 +336,26 @@ class Solution {
 ```
 
 Python：
-
-
+```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
+//递归法
+class Solution:
+    def isValidBST(self, root: TreeNode) -> bool:
+        res = []  //把二叉搜索树按中序遍历写成list
+        def buildalist(root):
+            if not root: return  
+            buildalist(root.left)  //左
+            res.append(root.val)  //中
+            buildalist(root.right)  //右
+            return res  
+        buildalist(root)
+        return res == sorted(res) and len(set(res)) == len(res) //检查list里的数有没有重复元素，以及是否按从小到大排列
+```
 Go：
 ```Go
 import "math"