validate-binary-search-tree solution

Author: yuhyeon99

validate-binary-search-tree/yuhyeon99.js

@@ -0,0 +1,23 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+var isValidBST = function(root) {
+    function dfs(node, low, high) {
+        if(!node) return true;
+
+        if(!(low < node.val && node.val < high)) return false;
+
+        return dfs(node.left, low, node.val) && dfs(node.right, node.val, high);
+    }
+
+    return dfs(root, -Infinity, Infinity);
+};