symmetric-tree.md

<p>Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).</p>

<p>For example, this binary tree <code>[1,2,2,3,4,4,3]</code> is symmetric:</p>

<pre>
    1
   / \
  2   2
 / \ / \
3  4 4  3
</pre>

<p>&nbsp;</p>

<p>But the following <code>[1,2,2,null,3,null,3]</code> is not:</p>

<pre>
    1
   / \
  2   2
   \   \
   3    3
</pre>

<p>&nbsp;</p>

<p><b>Note:</b><br />
Bonus points if you could solve it both recursively and iteratively.</p>