2415 - Reverse Odd Levels of Binary Tree.

Medium

Given the root of a perfect binary tree, reverse the node values at each odd level of the tree.

• For example, suppose the node values at level 3 are [2,1,3,4,7,11,29,18], then it should become [18,29,11,7,4,3,1,2].

Return the root of the reversed tree.

A binary tree is perfect if all parent nodes have two children and all leaves are on the same level.

The level of a node is the number of edges along the path between it and the root node.

Example 1:

Input: root = 2,3,5,8,13,21,34

Output: 2,5,3,8,13,21,34

Explanation:

The tree has only one odd level.

The nodes at level 1 are 3, 5 respectively, which are reversed and become 5, 3.

Example 2:

Input: root = 7,13,11

Output: 7,11,13

Explanation:

The nodes at level 1 are 13, 11, which are reversed and become 11, 13.

Example 3:

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

Explanation:

The odd levels have non-zero values.

The nodes at level 1 were 1, 2, and are 2, 1 after the reversal.

The nodes at level 3 were 1, 1, 1, 1, 2, 2, 2, 2, and are 2, 2, 2, 2, 1, 1, 1, 1 after the reversal.

Constraints:

• The number of nodes in the tree is in the range <code>1, 2¹⁴</code>.

• <code>0 <= Node.val <= 10⁵</code>

• root is a perfect binary tree.