Is Maximum Level Sum of a Binary Tree easy or hard?

Maximum Level Sum of a Binary Tree is considered a Medium difficulty problem on LeetCode. The logic is straightforward if you understand BFS level-order traversal, but recognizing the level-based processing pattern is the key challenge.

Maximum Level Sum of a Binary Tree Python/Java solution

Python and Java implementations typically use BFS with a queue. Each iteration processes all nodes at the current level, calculates the sum, and enqueues child nodes. The same logic can be implemented in C++, C#, and JavaScript with similar queue-based structures.

How to solve Maximum Level Sum of a Binary Tree in O(n)?

Traverse the tree once and accumulate the sum of node values for each level. Using BFS, process nodes in a queue level by level and track the maximum sum encountered. Using DFS, store cumulative sums in an array indexed by depth and compute the maximum after traversal.

What is the best approach for Maximum Level Sum of a Binary Tree?

Breadth-First Search (BFS) using level-order traversal is the most common solution. A queue processes nodes level by level, allowing you to compute the sum of each level in one pass. This approach runs in O(n) time and uses O(w) space where w is the maximum width of the tree.

Is Maximum Level Sum of a Binary Tree asked at Google/Amazon/Meta?

Tree traversal problems that involve level processing frequently appear in interviews at companies like Amazon, Google, and Meta. Variations of level-order traversal and BFS-based tree aggregation are common interview patterns.

What data structure is used in Maximum Level Sum of a Binary Tree?

The BFS approach relies on a queue to perform level-order traversal. The DFS approach uses recursion and an array or list to store sums for each level while traversing the tree.

What is the time complexity of Maximum Level Sum of a Binary Tree?

The optimal solutions run in O(n) time because every node in the binary tree is visited exactly once. BFS processes nodes level by level, while DFS processes nodes through recursion but still touches each node once.

Description Hints 4 Solution Video 20:01

1161. Maximum Level Sum of a Binary Tree

Medium70.0% acceptance4 companies

Given the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on.

Return the smallest level x such that the sum of all the values of nodes at level x is maximal.

Example 1:

Input: root = [1,7,0,7,-8,null,null]
Output: 2
Explanation: 
Level 1 sum = 1.
Level 2 sum = 7 + 0 = 7.
Level 3 sum = 7 + -8 = -1.
So we return the level with the maximum sum which is level 2.

Example 2:

Input: root = [989,null,10250,98693,-89388,null,null,null,-32127]
Output: 2

Constraints:

The number of nodes in the tree is in the range [1, 10⁴].
-10⁵ <= Node.val <= 10⁵

Asked at 4 companies

Google Meta Amazon Microsoft

Topics

Hints open one at a time

Hint 1

Calculate the sum for each level then find the level with the maximum sum.

Hint 2

How can you traverse the tree ?

Hint 3

How can you sum up the values for every level ?

Hint 4

Use DFS or BFS to traverse the tree keeping the level of each node, and sum up those values with a map or a frequency array.

20:01

Still stuck?Read 4 approaches, or watch a walkthrough.

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