Reverse Odd Levels of Binary Tree
<p>Given the <code>root</code> of a <strong>perfect</strong> binary tree, reverse the node values at each <strong>odd</strong> level of the tree.</p>

<ul>
	<li>For example, suppose the node values at level 3 are <code>[2,1,3,4,7,11,29,18]</code>, then it should become <code>[18,29,11,7,4,3,1,2]</code>.</li>
</ul>

<p>Return <em>the root of the reversed tree</em>.</p>

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

<p>The <strong>level</strong> of a node is the number of edges along the path between it and the root node.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2400-2499/2415.Reverse%20Odd%20Levels%20of%20Binary%20Tree/images/first_case1.png" style="width: 626px; height: 191px;" />
<pre>
<strong>Input:</strong> root = [2,3,5,8,13,21,34]
<strong>Output:</strong> [2,5,3,8,13,21,34]
<strong>Explanation:</strong> 
The tree has only one odd level.
The nodes at level 1 are 3, 5 respectively, which are reversed and become 5, 3.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2400-2499/2415.Reverse%20Odd%20Levels%20of%20Binary%20Tree/images/second_case3.png" style="width: 591px; height: 111px;" />
<pre>
<strong>Input:</strong> root = [7,13,11]
<strong>Output:</strong> [7,11,13]
<strong>Explanation:</strong> 
The nodes at level 1 are 13, 11, which are reversed and become 11, 13.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> root = [0,1,2,0,0,0,0,1,1,1,1,2,2,2,2]
<strong>Output:</strong> [0,2,1,0,0,0,0,2,2,2,2,1,1,1,1]
<strong>Explanation:</strong> 
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.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 2<sup>14</sup>]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 10<sup>5</sup></code></li>
	<li><code>root</code> is a <strong>perfect</strong> binary tree.</li>
</ul>
Tree; Depth-First Search; Breadth-First Search; Binary Tree
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def reverseOddLevels(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        q = deque([root])
        i = 0
        while q:
            if i & 1:
                l, r = 0, len(q) - 1
                while l < r:
                    q[l].val, q[r].val = q[r].val, q[l].val
                    l, r = l + 1, r - 1
            for _ in range(len(q)):
                node = q.popleft()
                if node.left:
                    q.append(node.left)
                    q.append(node.right)
            i += 1
        return root
