1315. Sum of Nodes with Even-Valued Grandparent

Medium

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, 10^4].

• 1 <= Node.val <= 100

解題

透過將 parent、grandparent 節點傳下去的方式判斷是否需要加到 ans

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumEvenGrandparent(root *TreeNode) int {
    ans := 0

    var helper func(*TreeNode, *TreeNode, *TreeNode)
    helper = func(node *TreeNode, parent *TreeNode, grandParent *TreeNode) {
        if node == nil {
            return 
        }

        if grandParent != nil && grandParent.Val % 2 == 0 {
            ans += node.Val
        }

        helper(node.Left, node, parent)
        helper(node.Right, node, parent)
    }

    helper(root, nil, nil)

    return ans
}