update: 98

Author: hijiangtao

README.md

@@ -52,6 +52,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |88|[	Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array/) | [JavaScript](./src/merge-sorted-array/res.js)|Medium|
 |91|[Decode Ways](https://leetcode.com/problems/decode-ways/) | [JavaScript](./src/decode-ways/res.js)|Medium|
 |93|[Restore IP Addresses](https://leetcode.com/problems/restore-ip-addresses/) | [JavaScript](./src/restore-ip-addresses/res.js)|Medium|
+|98|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/) | [JavaScript](./src/validate-binary-search-tree/res.js)|Medium|
 |100|[Same Tree](https://leetcode.com/problems/same-tree/) | [JavaScript](./src/same-tree/res.js)|Easy|
 |101|[Symmetric Tree](https://leetcode.com/problems/symmetric-tree/) | [JavaScript](./src/symmetric-tree/res.js)|Easy|
 |102|[Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/) | [JavaScript](./src/binary-tree-level-order-traversal/res.js)|Medium|

src/validate-binary-search-tree/res.js

@@ -0,0 +1,27 @@
+/**
+ * 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;
+
+  const validSubBST = (element, low, high) => {
+    if (low !== null && low >= element.val) return false;
+    if (high !== null && high <= element.val) return false;
+    if (!element.left && !element.right) return true;
+    
+    if (element.left && !validSubBST(element.left, low, element.val)) return false;
+    if (element.right && !validSubBST(element.right, element.val, high)) return false;
+    
+    return true;
+  }
+
+  return validSubBST(root, null, null);
+};