1public class TreeNode {
2    public int val;
3    public TreeNode left;
4    public TreeNode right;
5    public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
6        this.val = val;
7        this.left = left;
8        this.right = right;
9    }
10}
11
12public class Solution {
13    public int SumEvenGrandparent(TreeNode root) {
14        return DFS(root, null, null);
15    }
16
17    private int DFS(TreeNode node, TreeNode parent, TreeNode grandparent) {
18        if (node == null) return 0;
19        int sum = 0;
20        if (grandparent != null && grandparent.val % 2 == 0) {
21            sum += node.val;
22        }
23        sum += DFS(node.left, node, parent);
24        sum += DFS(node.right, node, parent);
25        return sum;
26    }
27}