Sum of Nodes with Even-Valued Grandparent

Problem Description

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

Solution (JavaScript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var sumEvenGrandparent = function(root) {
    const sum = (n, p, gp) => {
        if(!n) return 0;
        const v = gp%2 === 0 ? n.val : 0;
        return v + sum(n.left, n.val, p) + sum(n.right, n.val, p);
    }
    return sum(root, 1, 1);
};