Question
Given a binary tree as a level-order array `arr` (using `null` for missing children, so JSON null arrives as Python None), find the maximum path sum. A path is any sequence of nodes connected by parent-child edges; it need not pass through the root and must contain at least one node. Node values may be negative. The tree is non-empty. `1 <= node count <= 30000`.
max_path_sum(arr: list[int]) → int[[1,2,3]]out6State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.