Breadth-First Search/Maximum Level Sum of a Binary TreeEasy

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Maximum Level Sum of a Binary Tree

Breadth-First Search·Easy

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.

Input convention. The tree is passed as a level-order array with null for missing children (LeetCode serialization). The starter includes TreeNode and arrayToTree. Use a BFS to walk levels — that's the canonical pattern this exercise drills.

If the tree is empty, return 0.

Examples

Input: values = [1,7,0,7,-8,null,null]

Output: 2

Level 1 sum = 1, Level 2 sum = 7 + 0 = 7, Level 3 sum = 7 + (-8) = -1. Level 2 has the maximum.

Input: values = [989,null,10250,98693,-89388,null,null,null,-32127]

Output: 2

Constraints

The number of nodes in the tree is in the range [0, 10^4].
-10^5 <= Node.val <= 10^5

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Tests

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Passed32 ms

First attempt — retry to track metric movement here.

Your approach

Pattern:Breadth-First Search
Time:O(N)
Space:O(1)

Complete approach — pattern and complexity both named.

Coach

What you got right

You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.

Where it diverged

No divergence detected. The code correctly aligns with the stated approach.

Next attempt: focus on

Try solving related sliding window problems to build familiarity with two-pointer variants.

Signals

No signals fired — clean run, you stayed in flow.