If a node in a binary tree is not containing left or right child or it is a leaf node then that absence of child node can be represented by the null pointers. The space engaged by these null entries can be utilized to store any kind of valuable information. One possible way to utilize or use this space is to have special pointer that point to nodes higher in the tree that is ancestors. Such special pointers are called threads and the binary tree having such pointers is called as threaded binary tree. There are various ways to thread a binary tree each of these ways either correspond either in-order or pre-order traversal of T. A Threaded Binary Tree is a type of binary tree in which every node that does not have a right child has a THREAD (or a link) to its INORDER successor. By doing this threading we avoid the recursive method of traversing a Tree, which makes use of stacks and wastes a lot of time and memory.
The node structure for a threaded binary tree differs a bit and its like this
struct NODE *leftchild;
struct NODE *rightchild;
struct NODE *thread;
The Threaded Binary tree made from normal binary tree...
The INORDER traversal for the above drawn tree is -- D B A E C. Then the respective
Threaded Binary tree will be --
B does not have right child and its inorder successor is A and so a thread has been made in between them. Likewise, for D and E. C have no right child but it has no inorder successor even, therefore it has a hanging thread.