solve validate binary search tree

Author: JangAyeon

validate-binary-search-tree/JangAyeon.js

@@ -0,0 +1,28 @@
+/**
+ * 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}
+ */
+const dfs = (node, left, right) => {
+  if (!node) {
+    return true;
+  }
+
+  return (
+    node.val > left &&
+    node.val < right &&
+    dfs(node.left, left, node.val) &&
+    dfs(node.right, node.val, right)
+  );
+};
+
+const isValidBST = function (root) {
+  return dfs(root, -Infinity, Infinity);
+};