Formatted question description: https://leetcode.ca/all/1315.html

1315. Sum of Nodes with Even-Valued Grandparent (Medium)

Given a binary tree, return the sum of values of nodes with even-valued grandparent.  (A grandparent of a node is the parent of its parent, if it exists.)

If there are no nodes with an even-valued grandparent, return 0.

 

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.

 

Constraints:

• The number of nodes in the tree is between 1 and 10^4.
• The value of nodes is between 1 and 100.

Related Topics:
Tree, Depth-first Search

Solution 1. Pre-order Traversal

// OJ: https://leetcode.com/problems/sum-of-nodes-with-even-valued-grandparent/

// Time: O(N)
// Space: O(N)
class Solution {
    int ans = 0;
    vector<TreeNode*> v;
    void preorder(TreeNode *root, int level) {
        if (!root) return;
        if (v.size() <= level) v.push_back(root);
        else v[level] = root;
        if (level - 2 >= 0 && v[level - 2]->val % 2 == 0) ans += root->val;
        preorder(root->left, level + 1);
        preorder(root->right, level + 1);
    }
public:
    int sumEvenGrandparent(TreeNode* root) {
        preorder(root, 0);
        return ans;
    }
};

Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int sumEvenGrandparent(TreeNode root) {
        int sum = 0;
        Queue<TreeNode> nodeQueue = new LinkedList<TreeNode>();
        Queue<Boolean> booleanQueue = new LinkedList<Boolean>();
        nodeQueue.offer(root);
        booleanQueue.offer(false);
        while (!nodeQueue.isEmpty()) {
            TreeNode node = nodeQueue.poll();
            boolean isEven = booleanQueue.poll();
            boolean curEven = node.val % 2 == 0;
            TreeNode left = node.left, right = node.right;
            if (left != null) {
                if (isEven)
                    sum += left.val;
                nodeQueue.offer(left);
                booleanQueue.offer(curEven);
            }
            if (right != null) {
                if (isEven)
                    sum += right.val;
                nodeQueue.offer(right);
                booleanQueue.offer(curEven);
            }
        }
        return sum;
    }
}

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