public class Solution
extends Object
1315 - Sum of Nodes with Even-Valued Grandparent\.
Medium
Given the `root` of a binary tree, return _the sum of values of nodes with an **even-valued grandparent**_. If there are no nodes with an **even-valued grandparent** , return `0`.
A **grandparent** of a node is the parent of its parent if it exists.
**Example 1:**
**Input:** root = [6,7,8,2,7,1,3,9,null,1,4,null,null,null,5]
**Output:** 18
**Explanation:** The red nodes are the nodes with even-value grandparent while the blue nodes are the even-value grandparents.
**Example 2:**
**Input:** root = [1]
**Output:** 0
**Constraints:**
* The number of nodes in the tree is in the range [1, 104].
* `1 <= Node.val <= 100`