Add solution #144

Author: JoshCrozier

Diff for: README.md

@@ -45,6 +45,7 @@
 121|[Best Time to Buy and Sell Stock](./0121-best-time-to-buy-and-sell-stock.js)|Easy|
 136|[Single Number](./0136-single-number.js)|Easy|
 141|[Linked List Cycle](./0141-linked-list-cycle.js)|Easy|
+144|[Binary Tree Preorder Traversal](./0144-binary-tree-preorder-traversal.js)|Easy|
 151|[Reverse Words in a String](./0151-reverse-words-in-a-string.js)|Medium|
 152|[Maximum Product Subarray](./0152-maximum-product-subarray.js)|Medium|
 203|[Remove Linked List Elements](./0203-remove-linked-list-elements.js)|Easy|

Diff for: solutions/0144-binary-tree-preorder-traversal.js

@@ -0,0 +1,25 @@
+/**
+ * 144. Binary Tree Preorder Traversal
+ * https://leetcode.com/problems/binary-tree-preorder-traversal/
+ * Difficulty: Easy
+ *
+ * Given the root of a binary tree, return the preorder traversal of its nodes' values.
+ */
+
+/**
+ * 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 {number[]}
+ */
+var preorderTraversal = function(root) {
+  return root
+    ? [root.val, ...preorderTraversal(root.left), ...preorderTraversal(root.right)]
+    : [];
+};