1522. Diameter of N-Ary Tree

Given a root of an N-ary tree, you need to compute the length of the diameter of the tree.

The diameter of an N-ary tree is the length of the longest path between any two nodes in the tree. This path may or may not pass through the root.

(Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value.)

Example 1:

Input: root = [1,null,3,2,4,null,5,6]
Output: 3
Explanation: Diameter is shown in red color.

Example 2:

Input: root = [1,null,2,null,3,4,null,5,null,6]
Output: 4

Example 3:

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: 7

 1 class Solution {
 2     int max = 0;
 3     public int diameter(Node root) {
 4         max = 0;
 5         getDiameter(root);
 6         return max;
 7     }
 8 
 9     private int getDiameter(Node node) {
10         if(node == null) {
11             return 0;
12         }
13         List children = node.children;
14         int maxOne = 0; // max from all children
15         int maxTwo = 0; // second max from all children
16         for (Node child :children) {
17             int res = getDiameter(child);
18             if (res > maxOne) {
19                 maxTwo = maxOne;
20                 maxOne = res;
21             } else if (res > maxTwo) {
22                 maxTwo = res;
23             }
24         }
25         max = Math.max(max, maxOne + maxTwo);
26         return maxOne + 1;
27     }
28 }