1315. Sum of Nodes with Even-Valued Grandparent

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

---

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sumEvenGrandparent(self, root: TreeNode) -> int:
        self.ans=0
        
        def dfs(node, gp, p):
            if not node:
                return
            
            if gp:
                self.ans+=node.val
            iseven=node.val%2==0
            dfs(node.left, p, iseven)
            dfs(node.right, p, iseven)
        dfs(root,False,False)
        
        return self.ans