Given a binary tree, write a program to flatten it to a linked list. The flattening of the binary tree should be in-place.
Problem Note
- Note that the left child of all nodes should be NULL.
For example
Input: Given the following binary tree
4
/ \
5 8
/ \ \
6 7 9
Output: The flattened tree should look like:
4
\
5
\
6
\
7
\
8
\
9