Back with another question today, this one's a little harder then the other ones.

I want to easily go through a binary tree without having to traverse it in a tree way, so I'm going to ask you to flatten the tree. A flattened tree is similar to the binary tree execpt it uses its left and right pointers like a doubly linked list.

Here's an example:

    10
   /  \
  5    15
 / \     \
1   11    19

The tree after being flattened would look like:

1 <-> 5 <-> 11 <-> 10 <-> 19 <-> 15

Assume your class (if your working with Java) looks like this:

    static class BinaryTree {
        int value;
        BinaryTree left = null;
        BinaryTree right = null;

        public BinaryTree(int value) {
            this.value = value;
        }
    }