Update 98.validate-binary-search-tree.md

validate-binary-search-tree 定义法添加js代码实现

Author: TH-coder

problems/98.validate-binary-search-tree.md

@@ -185,7 +185,7 @@ class Solution {
 
 ### 定义法
 
-* 语言支持：C++，Python3, Java
+* 语言支持：C++，Python3, Java, JS
 
 C++ Code：
 
@@ -311,6 +311,34 @@ class Solution {
 }
 ```
 
+JS Code:
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+var isValidBST = function(root) {
+  if(!root)return true;
+  return valid(root);
+};
+
+function valid(root,min = -Infinity,max=Infinity){
+  if(!root)return true;
+  const val = root.val;
+  if(val<=min)return false;
+  if(val>=max)return false;
+  return valid(root.left,min,Math.min(val,max))&&valid(root.right,Math.max(val,min),max)
+}
+```
+
 ## 相关题目
 
 [230.kth-smallest-element-in-a-bst](./230.kth-smallest-element-in-a-bst.md)