Add Values Whose Grandparent Is Even
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
For each native binary-tree node, inspect its grandparent, meaning its parent's parent when it exists. Return the sum of values of exactly those nodes whose grandparent value is even. Return 0 if there are none.
```cpp
class Solution {
public:
int sumEvenGrandparent(TreeNode* root);
};
```
### Examples
**Example 1:**
```text
Input: root = [2,3,4,5,6]
Output: 11
Explanation: Nodes5 and6 have even-valued grandparent2, so their values sum to11.
```
**Example 2:**
```text
Input: root = [1,2,3,4]
Output: 0
Explanation: The only node with a grandparent is4, whose grandparent1 is odd.
```
### Constraints
- The tree has 1 to 10000 nodes.
- Each node value is an integer from 1 through 100.
### Contract considerations
Retain the native TreeNode pointer and do not reinterpret an array-index grandparent formula for an arbitrary tree.
```hint Read the boundary condition
Distinguish a qualifying grandparent from a qualifying parent. Include nodes that have no grandparent.
```
### Boundary reminders
Retain the native TreeNode pointer and do not reinterpret an array-index grandparent formula for an arbitrary tree.
Overview: Add Values Whose Grandparent Is Even. For each native binary-tree node, inspect its grandparent, meaning its parent's parent when it exists.
