1
const dfs = function (node, evenParent) {
2
  if (!node) return 0;
3

4
  const isEvenNode = node.val % 2 === 0;
5

6
  const left = dfs(node.left, isEvenNode);
7
  const right = dfs(node.right, isEvenNode);
8

9
  if (!evenParent) return left + right;
10
  return (
11
    left +
12
    right +
13
    (node.left ? node.left.val : 0) +
14
    (node.right ? node.right.val : 0)
15
  );
16
};
17

18
var sumEvenGrandparent = function (root) {
19
  if (!root) return 0;
20
  return dfs(root, false);
21
};