Grandchildren of Even Ancestors

Medium

You are given the root of a binary tree. Add up the values of every node whose grandparent (the parent of its parent) exists and holds an even number. If no node qualifies, return 0.

Example 1

root=tree_node([4, 3, 5, 1, 9, None, 7]) → 17

The root 4 is even and its grandchildren are 1, 9 and 7: 1 + 9 + 7 = 17. No other node has grandchildren.

Example 2

root=tree_node([3, 6, None, 2, 8, 5]) → 5

The root 3 is odd, so its grandchildren 2 and 8 do not count. The even node 6 has one grandchild, 5, so the answer is 5.

Example 3

root=tree_node([10, 20]) → 0

The tree has only two levels, so nobody has a grandchild.

Constraints

1 ≤ number of nodes ≤ 10⁴
1 ≤ Node.val ≤ 100

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Topics

Tree Depth-First Search Breadth-First Search Binary Tree

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Input

root=tree_node([4, 3, 5, 1, 9, None, 7])

Expected

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