symmetric-tree

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Algorithms

Given the <code>root</code> of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/symtree1.jpg" style="width: 354px; height: 291px;" />
<pre>
Input: root = [1,2,2,3,4,4,3]
Output: true
</pre>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/symtree2.jpg" style="width: 308px; height: 258px;" />
<pre>
Input: root = [1,2,2,null,3,null,3]
Output: false
</pre>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 1000]</code>.</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</code></li>
</ul>

&nbsp;
Follow up: Could you solve it both recursively and iteratively?

isSymmetric

Symmetric Tree

Tree

Depth-First Search

Breadth-First Search

Binary Tree

给你一个二叉树的根节点 <code>root</code> ， 检查它是否轴对称。

&nbsp;

示例 1：
<img alt="" src="https://pic.leetcode.cn/1698026966-JDYPDU-image.png" style="width: 354px; height: 291px;" />
<pre>
输入：root = [1,2,2,3,4,4,3]
输出：true
</pre>

示例 2：
<img alt="" src="https://pic.leetcode.cn/1698027008-nPFLbM-image.png" style="width: 308px; height: 258px;" />
<pre>
输入：root = [1,2,2,null,3,null,3]
输出：false
</pre>

&nbsp;

提示：

<ul>
	<li>树中节点数目在范围 <code>[1, 1000]</code> 内</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</code></li>
</ul>

&nbsp;

进阶：你可以运用递归和迭代两种方法解决这个问题吗？