Create 98-validate-binary-search-tree.js

Author: everthis

98-validate-binary-search-tree.js

@@ -0,0 +1,23 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+const isValidBST = function(root) {
+  return helper(root, -Infinity, Infinity)
+}
+function helper(root, minValue, maxValue) {
+  if (!root) return true
+  if (root.val <= minValue || root.val >= maxValue) {
+    return false
+  }
+  let leftSide = helper(root.left, minValue, root.val)
+  let rightSide = helper(root.right, root.val, maxValue)
+  return leftSide && rightSide
+}