reverse-odd-levels-of-binary-tree

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Algorithms

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

<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>

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.

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2022/07/28/first_case1.png" style="width: 626px; height: 191px;" />
<pre>
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.
</pre>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2022/07/28/second_case3.png" style="width: 591px; height: 111px;" />
<pre>
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.
</pre>

Example 3:

<pre>
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.
</pre>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 214]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 105</code></li>
	<li><code>root</code> is a perfect binary tree.</li>
</ul>

reverseOddLevels

Reverse Odd Levels of Binary Tree

Invert Binary Tree

invert-binary-tree

翻转二叉树

Tree

Depth-First Search

Breadth-First Search

Binary Tree

给你一棵 完美 二叉树的根节点 <code>root</code> ，请你反转这棵树中每个 奇数 层的节点值。

<ul>
	<li>例如，假设第 3 层的节点值是 <code>[2,1,3,4,7,11,29,18]</code> ，那么反转后它应该变成 <code>[18,29,11,7,4,3,1,2]</code> 。</li>
</ul>

反转后，返回树的根节点。

完美 二叉树需满足：二叉树的所有父节点都有两个子节点，且所有叶子节点都在同一层。

节点的 层数 等于该节点到根节点之间的边数。

&nbsp;

示例 1：
<img alt="" src="https://assets.leetcode.com/uploads/2022/07/28/first_case1.png" style="width: 626px; height: 191px;" />
<pre>
输入：root = [2,3,5,8,13,21,34]
输出：[2,5,3,8,13,21,34]
解释：
这棵树只有一个奇数层。
在第 1 层的节点分别是 3、5 ，反转后为 5、3 。
</pre>

示例 2：
<img alt="" src="https://assets.leetcode.com/uploads/2022/07/28/second_case3.png" style="width: 591px; height: 111px;" />
<pre>
输入：root = [7,13,11]
输出：[7,11,13]
解释： 
在第 1 层的节点分别是 13、11 ，反转后为 11、13 。 
</pre>

示例 3：

<pre>
输入：root = [0,1,2,0,0,0,0,1,1,1,1,2,2,2,2]
输出：[0,2,1,0,0,0,0,2,2,2,2,1,1,1,1]
解释：奇数层由非零值组成。
在第 1 层的节点分别是 1、2 ，反转后为 2、1 。
在第 3 层的节点分别是 1、1、1、1、2、2、2、2 ，反转后为 2、2、2、2、1、1、1、1 。
</pre>

&nbsp;

提示：

<ul>
	<li>树中的节点数目在范围 <code>[1, 214]</code> 内</li>
	<li><code>0 &lt;= Node.val &lt;= 105</code></li>
	<li><code>root</code> 是一棵 完美 二叉树</li>
</ul>