add python 98

python-leetcode/README.md

@@ -18,7 +18,7 @@
 4.  [二叉搜索树中的搜索](./solution/tree/leetcode_700_.py)
 5.  [N叉树的后续遍历](./solution/tree/leetcode_590_.py)
 6.  [二叉树的层次遍历](./solution/tree/leetcode_32_.py)
-7.  [递增顺序查找二叉树](./solution/tree/leetcode_897_.py)
+7.  [递增顺序查找二叉树](./solution/tree/leetcode_897_.py)F
 8.  [单值二叉树](./solution/tree/leetcode_965_.py)
 9.  [二叉树的层次遍历II](./solution/tree/leetcode_107_.py)
 10. [二叉树层的平均值](./solution/tree/leetcode_637_.py)
@@ -60,6 +60,7 @@
 46. [从前序与中序遍历序列构造二叉树](./solution/tree/leetcode_105_.py)
 47. [二叉树的前序遍历](./solution/tree/leetcode_144_.py)
 48. [N叉树的层序遍历](./solution/tree/leetcode_429_.py)
+49. [验证二叉搜索树](./solution/tree/leetcode_98_.py)
 
 
 

python-leetcode/solution/tree/leetcode_98_.py

+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# coding=utf-8
+"""
+98. 验证二叉搜索树
+"""
+from solution import TreeNode
+
+
+class Solution:
+    def isValidBST(self, root: TreeNode) -> bool:
+        temp = -2 ** 32
+
+        def dfs(root: TreeNode) -> bool:
+            nonlocal temp
+            if not root:
+                return True
+            a = dfs(root.left)
+            if root.val <= temp:
+                return False
+            temp = root.val
+            if a:
+                b = dfs(root.right)
+                return b
+            return a
+
+        return dfs(root)