Add solution #589

Author: JoshCrozier

README.md

@@ -295,6 +295,7 @@
 566|[Reshape the Matrix](./0566-reshape-the-matrix.js)|Easy|
 567|[Permutation in String](./0567-permutation-in-string.js)|Medium|
 575|[Distribute Candies](./0575-distribute-candies.js)|Easy|
+589|[N-ary Tree Preorder Traversal](./0589-n-ary-tree-preorder-traversal.js)|Easy|
 594|[Longest Harmonious Subsequence](./0594-longest-harmonious-subsequence.js)|Easy|
 599|[Minimum Index Sum of Two Lists](./0599-minimum-index-sum-of-two-lists.js)|Easy|
 605|[Can Place Flowers](./0605-can-place-flowers.js)|Easy|

solutions/0589-n-ary-tree-preorder-traversal.js

@@ -0,0 +1,26 @@
+/**
+ * 589. N-ary Tree Preorder Traversal
+ * https://leetcode.com/problems/n-ary-tree-preorder-traversal/
+ * Difficulty: Easy
+ *
+ * Given the root of an n-ary tree, return the preorder traversal of its nodes' values.
+ *
+ * Nary-Tree input serialization is represented in their level order traversal. Each group
+ * of children is separated by the null value (See examples)
+ */
+
+/**
+ * // Definition for a _Node.
+ * function _Node(val, children) {
+ *    this.val = val;
+ *    this.children = children;
+ * };
+ */
+
+/**
+ * @param {_Node|null} root
+ * @return {number[]}
+ */
+var preorder = function(root) {
+  return !root ? [] : [root.val, ...root.children.flatMap(n => preorder(n))];
+};