From 228b2409a80474eda01f3d16a722c53369e9c94e Mon Sep 17 00:00:00 2001
From: huangge1199 <huangge1199@hotmail.com>
Date: Wed, 11 Aug 2021 11:48:53 +0800
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 .../editor/cn/ValidateBinarySearchTree.java   | 81 +++++++++++++++++++
 .../editor/cn/ValidateBinarySearchTree.md     | 32 ++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.java
 create mode 100644 src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.md

diff --git a/src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.java b/src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.java
new file mode 100644
index 0000000..b593a46
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+++ b/src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.java
@@ -0,0 +1,81 @@
+//给定一个二叉树，判断其是否是一个有效的二叉搜索树。 
+//
+// 假设一个二叉搜索树具有如下特征： 
+//
+// 
+// 节点的左子树只包含小于当前节点的数。 
+// 节点的右子树只包含大于当前节点的数。 
+// 所有左子树和右子树自身必须也是二叉搜索树。 
+// 
+//
+// 示例 1: 
+//
+// 输入:
+//    2
+//   / \
+//  1   3
+//输出: true
+// 
+//
+// 示例 2: 
+//
+// 输入:
+//    5
+//   / \
+//  1   4
+//     / \
+//    3   6
+//输出: false
+//解释: 输入为: [5,1,4,null,null,3,6]。
+//     根节点的值为 5 ，但是其右子节点值为 4 。
+// 
+// Related Topics 树 深度优先搜索 二叉搜索树 二叉树 
+// 👍 1159 👎 0
+
+package leetcode.editor.cn;
+
+import com.code.leet.entiy.TreeNode;
+
+//98:验证二叉搜索树
+class ValidateBinarySearchTree {
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new ValidateBinarySearchTree().new Solution();
+    }
+
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+
+    /**
+     * Definition for a binary tree node.
+     * public class TreeNode {
+     * int val;
+     * TreeNode left;
+     * TreeNode right;
+     * TreeNode() {}
+     * TreeNode(int val) { this.val = val; }
+     * TreeNode(int val, TreeNode left, TreeNode right) {
+     * this.val = val;
+     * this.left = left;
+     * this.right = right;
+     * }
+     * }
+     */
+    class Solution {
+        public boolean isValidBST(TreeNode root) {
+            return dfs(root, Long.MIN_VALUE, Long.MAX_VALUE);
+        }
+
+        public boolean dfs(TreeNode node, long min, long max) {
+            if (node == null) {
+                return true;
+            }
+            if (node.val <= min || node.val >= max) {
+                return false;
+            }
+            return dfs(node.left, min, node.val) && dfs(node.right, node.val, max);
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}
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diff --git a/src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.md b/src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.md
new file mode 100644
index 0000000..752324f
--- /dev/null
+++ b/src/main/java/leetcode/editor/cn/ValidateBinarySearchTree.md
@@ -0,0 +1,32 @@
+<p>给定一个二叉树，判断其是否是一个有效的二叉搜索树。</p>
+
+<p>假设一个二叉搜索树具有如下特征：</p>
+
+<ul>
+	<li>节点的左子树只包含<strong>小于</strong>当前节点的数。</li>
+	<li>节点的右子树只包含<strong>大于</strong>当前节点的数。</li>
+	<li>所有左子树和右子树自身必须也是二叉搜索树。</li>
+</ul>
+
+<p><strong>示例&nbsp;1:</strong></p>
+
+<pre><strong>输入:</strong>
+    2
+   / \
+  1   3
+<strong>输出:</strong> true
+</pre>
+
+<p><strong>示例&nbsp;2:</strong></p>
+
+<pre><strong>输入:
+</strong>    5
+   / \
+  1   4
+&nbsp;    / \
+&nbsp;   3   6
+<strong>输出:</strong> false
+<strong>解释:</strong> 输入为: [5,1,4,null,null,3,6]。
+&nbsp;    根节点的值为 5 ，但是其右子节点值为 4 。
+</pre>
+<div><div>Related Topics</div><div><li>树</li><li>深度优先搜索</li><li>二叉搜索树</li><li>二叉树</li></div></div>\n<div><li>👍 1159</li><li>👎 0</li></div>
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