1
class Solution {
2
  int sum = 0;
3

4
  public int sumEvenGrandparent(TreeNode root) {
5
    dfs(root, null, null);
6
    return sum;
7
  }
8

9
  void dfs(TreeNode current, TreeNode parent, TreeNode grandParent) {
10
    if (current == null) return; // base case
11
    if (grandParent != null && grandParent.val % 2 == 0) {
12
      sum += current.val;
13
    }
14

15
    // cur->cur.left ||cur.right , parent=cur,grandPrarent=parent
16
    dfs(current.left, current, parent);
17
    dfs(current.right, current, parent);
18
  }
19
}