How do you solve Sum of Nodes with Even-Valued Grandparent on LeetCode?

Sum of Nodes with Even-Valued Grandparent (LeetCode #1315) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding the relationship between nodes is crucial for tree problems.

What is the brute force solution for Sum of Nodes with Even-Valued Grandparent?

The brute force approach for Sum of Nodes with Even-Valued Grandparent is Brute Force, with O(n²) time complexity and O(1) space complexity. In this approach, we will traverse the entire tree and check each node's grandparent. If the grandparent's value is even, we add the current node's value to our sum. This method is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What are the interview tips for Sum of Nodes with Even-Valued Grandparent?

Always clarify the problem statement and constraints before jumping into coding. Discuss your thought process and approach with the interviewer. Consider edge cases, such as trees with only one node or all nodes having odd values.

What are common mistakes when solving Sum of Nodes with Even-Valued Grandparent?

Not properly checking for null nodes, which can lead to null pointer exceptions. Failing to track the parent and grandparent correctly during traversal.

#1315

Sum of Nodes with Even-Valued Grandparent

Medium

TreeDepth-First SearchBreadth-First SearchBinary TreeDepth-First Search (DFS)Recursion

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

This approach improves efficiency by using a single traversal of the tree while keeping track of the parent and grandparent nodes. This avoids redundant checks and allows us to compute the sum in linear time.

⚙️

Algorithm

4 steps

1Step 1: Perform a depth-first traversal of the tree starting from the root.
2Step 2: For each node, check if its grandparent exists and if its value is even.
3Step 3: If the grandparent is even, add the current node's value to a running total.
4Step 4: Pass the current node as the parent and the previous parent as the grandparent for the next recursive calls.

solution.py18 lines

1# Full working Python code
2class TreeNode:
3    def __init__(self, val=0, left=None, right=None):
4        self.val = val
5        self.left = left
6        self.right = right
7
8class Solution:
9    def sumEvenGrandparent(self, root: TreeNode) -> int:
10        def dfs(node, parent, grandparent):
11            if not node:
12                return 0
13            total = 0
14            if grandparent and grandparent.val % 2 == 0:
15                total += node.val
16            total += dfs(node.left, node, parent) + dfs(node.right, node, parent)
17            return total
18        return dfs(root, None, None)

ℹ

Complexity note: The time complexity is O(n) because we visit each node exactly once. The space complexity is O(n) due to the recursion stack in the worst case (for a skewed tree).

1Understanding the relationship between nodes is crucial for tree problems.
2Recursion can simplify the traversal logic significantly.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.