1315

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
int ans = 0;
public:
    int sumEvenGrandparent(TreeNode* root) {
        dfs(root, NULL, NULL);
        return ans;
    }
    void dfs(TreeNode* current, TreeNode* parent, TreeNode* gparent){
        if(!current) return;
        if(gparent && gparent->val % 2 == 0)
            ans += current->val;
        dfs(current->left, current, parent);
        dfs(current->right, current, parent);
    }
};