Reverse Odd Levels of Binary Tree

MediumTreeslevel order

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

You are given the root of a **perfect** binary tree: every internal node has two children and all leaves are on the same level. Levels are numbered from 0 at the root. For every **odd** level, reverse the order of the node values on that level. For example, a level reading [2,1,3,4,7,11,29,18] becomes [18,29,11,7,4,3,1,2]. Only the values move; the tree shape stays the same. Return the root of the modified tree.

Examples

Input: root = [2,3,5,8,13,21,34]
Output: [2,5,3,8,13,21,34]
Level 1 reads 3, 5 and becomes 5, 3. Level 2 is even, so it is unchanged.
Input: root = [7,13,11]
Output: [7,11,13]
Only level 1 is reversed.
Input: root = [0,1,2,0,0,0,0,1,1,1,1,2,2,2,2]
Output: [0,2,1,0,0,0,0,2,2,2,2,1,1,1,1]
Levels 1 and 3 are reversed.

Constraints

  • 1 <= number of nodes <= 2^14
  • The number of nodes is `2^k - 1` for some `k >= 1`
  • 0 <= Node.val <= 10^5

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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