flatten-binary-tree-to-linked-list.md

<p>Given a binary tree, flatten it to a linked list in-place.</p>

<p>For example, given the following tree:</p>

<pre>
    1
   / \
  2   5
 / \   \
3   4   6
</pre>

<p>The flattened tree should look like:</p>

<pre>
1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6
</pre>