Add solution #559

Author: JoshCrozier

README.md

@@ -443,6 +443,7 @@
 556|[Next Greater Element III](./0556-next-greater-element-iii.js)|Medium|
 557|[Reverse Words in a String III](./0557-reverse-words-in-a-string-iii.js)|Easy|
 558|[Logical OR of Two Binary Grids Represented as Quad-Trees](./0558-logical-or-of-two-binary-grids-represented-as-quad-trees.js)|Medium|
+559|[Maximum Depth of N-ary Tree](./0559-maximum-depth-of-n-ary-tree.js)|Easy|
 560|[Subarray Sum Equals K](./0560-subarray-sum-equals-k.js)|Medium|
 563|[Binary Tree Tilt](./0563-binary-tree-tilt.js)|Easy|
 565|[Array Nesting](./0565-array-nesting.js)|Medium|

solutions/0559-maximum-depth-of-n-ary-tree.js

@@ -0,0 +1,31 @@
+/**
+ * 559. Maximum Depth of N-ary Tree
+ * https://leetcode.com/problems/maximum-depth-of-n-ary-tree/
+ * Difficulty: Easy
+ *
+ * Given a n-ary tree, find its maximum depth.
+ *
+ * The maximum depth is the number of nodes along the longest path from the root node down to
+ * the farthest leaf node.
+ *
+ * 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 === undefined ? null : val;
+ *    this.children = children === undefined ? null : children;
+ * };
+ */
+
+/**
+ * @param {_Node|null} root
+ * @return {number}
+ */
+var maxDepth = function(root) {
+  if (!root) return 0;
+  if (!root.children || !root.children.length) return 1;
+  return Math.max(...root.children.map(child => maxDepth(child))) + 1;
+};