Given a Binary Tree (or BST).
1. Flatten the BT into a single link in the order of inorder traversal.
2. Flatten the BT into a single link in the order of preorder traversal.
3. Flatten the BST to sorted single linked list.
4. Flatten a BST to Double Linked List
5. Flatten a BST to Circular Double Linked List
6. Convert Sorted Linked List to BST.
7. Convert heap ordered Linked List to BT.