From cd37799b72126f0365358375133e460bbb1411b4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=97=A4=E9=9C=B2?= <080301087@163.com>
Date: Thu, 8 Jul 2021 16:04:46 +0800
Subject: [PATCH 1/2] =?UTF-8?q?Update=200098.=E9=AA=8C=E8=AF=81=E4=BA=8C?=
 =?UTF-8?q?=E5=8F=89=E6=90=9C=E7=B4=A2=E6=A0=91.md=20-=20=E5=A2=9E?=
 =?UTF-8?q?=E5=8A=A0=E4=BA=86python3=E7=89=88=E6=9C=AC=E7=9A=84=E7=AE=80?=
 =?UTF-8?q?=E5=8D=95=E9=80=92=E5=BD=92=E6=B3=95=E5=92=8C=E8=BF=AD=E4=BB=A3?=
 =?UTF-8?q?=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0098.验证二叉搜索树.md | 31 +++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/problems/0098.验证二叉搜索树.md b/problems/0098.验证二叉搜索树.md
index b93d8cd5..4652fb86 100644
--- a/problems/0098.验证二叉搜索树.md
+++ b/problems/0098.验证二叉搜索树.md
@@ -343,7 +343,7 @@ Python：
 #         self.val = val
 #         self.left = left
 #         self.right = right
-//递归法
+# 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
@@ -355,6 +355,35 @@ class Solution:
             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
+
+# 简单递归法
+class Solution:
+    def isValidBST(self, root: TreeNode) -> bool:
+        def isBST(root, min_val, max_val):
+            if not root: return True
+            if root.val >= max_val or root.val <= min_val:
+                return False
+            return isBST(root.left, min_val, root.val) and isBST(root.right, root.val, max_val)
+        return isBST(root, float("-inf"), float("inf"))
+
+# 迭代-中序遍历
+class Solution:
+    def isValidBST(self, root: TreeNode) -> bool:
+        stack = []
+        cur = root
+        pre = None
+        while cur or stack:
+            if cur: # 指针来访问节点，访问到最底层
+                stack.append(cur)
+                cur = cur.left
+            else: # 逐一处理节点
+                cur = stack.pop()
+                if pre and cur.val <= pre.val: # 比较当前节点和前节点的值的大小
+                    return False
+                pre = cur 
+                cur = cur.right
+        return True
+
 ```
 Go：
 ```Go

From 3ab914332ebfe60020061d2bc4bd9102687f4841 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=97=A4=E9=9C=B2?= <080301087@163.com>
Date: Thu, 8 Jul 2021 17:02:29 +0800
Subject: [PATCH 2/2] =?UTF-8?q?Update=200530.=E4=BA=8C=E5=8F=89=E6=90=9C?=
 =?UTF-8?q?=E7=B4=A2=E6=A0=91=E7=9A=84=E6=9C=80=E5=B0=8F=E7=BB=9D=E5=AF=B9?=
 =?UTF-8?q?=E5=B7=AE.md=20-=20=E5=A2=9E=E5=8A=A0=E4=BA=86python3=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC=E7=9A=84=E8=BF=AD=E4=BB=A3=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../0530.二叉搜索树的最小绝对差.md | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/problems/0530.二叉搜索树的最小绝对差.md b/problems/0530.二叉搜索树的最小绝对差.md
index 47b2b434..bf646443 100644
--- a/problems/0530.二叉搜索树的最小绝对差.md
+++ b/problems/0530.二叉搜索树的最小绝对差.md
@@ -222,6 +222,26 @@ class Solution:
         for i in range(len(res)-1):  // 统计有序数组的最小差值
             r = min(abs(res[i]-res[i+1]),r)
         return r
+        
+# 迭代法-中序遍历
+class Solution:
+    def getMinimumDifference(self, root: TreeNode) -> int:
+        stack = []
+        cur = root
+        pre = None
+        result = float('inf')
+        while cur or stack:
+            if cur: # 指针来访问节点，访问到最底层
+                stack.append(cur)
+                cur = cur.left
+            else: # 逐一处理节点
+                cur = stack.pop()
+                if pre: # 当前节点和前节点的值的差值
+                    result = min(result, cur.val - pre.val)
+                pre = cur
+                cur = cur.right
+        return result
+        
 ```
 Go：
 > 中序遍历，然后计算最小差值