1315. Sum of Nodes with Even-Valued Grandparent

Given a binary tree, return the sum of values of nodes with even-valued grandparent.  (A grandparent of a node is the parent of its parent, if it exists.)

If there are no nodes with an even-valued grandparent, return 0.

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.

Constraints:

• The number of nodes in the tree is between 1 and 10^4.
• The value of nodes is between 1 and 100.

class Solution {
   public int sumEvenGrandparent(TreeNode root) {
        return helper(root, 1, 1);
    }

    public int helper(TreeNode node, int p, int gp) {
        if (node == null) return 0;
        return helper(node.left, node.val, p) + helper(node.right, node.val, p) + (gp % 2 == 0 ? node.val : 0);
    }
}

开眼了 https://leetcode.com/problems/sum-of-nodes-with-even-valued-grandparent/discuss/477048/JavaC%2B%2BPython-1-Line-Recursive-Solution