data structures using in the linked representationa number of nodes contain null pointereither in their left or right fields or in both this space that is wasted in storing null pointer can be efficiently used to store some other useful piece of information for examplethe null entries can be replaced to store pointer to the in-order predecessor or the in-order figure linked representation of binary tree successor of the node these special pointers are called threads and binary trees containing threads are called threaded trees in the linked representation of threaded binary treethreads will be denoted using arrows there are many ways of threading binary tree and each type may vary according to the way the tree is traversed in this book we will discuss in-order traversal of the tree apart from thisa threaded binary tree may figure (abinary tree without threading correspond to one-way threading or two way threading in one-way threadinga thread will appear either in the right field or the left field of the node one-way threaded tree is also called single-threaded tree if the thread appears in the left fieldthen the left field will be made to point to the in-order predecessor of the node such one-way threaded tree is called figure (blinked representation of the binary tree left-threaded binary tree on the contrary(without threadingif the thread appears in the right fieldthen it will point to the in-order successor of the node such one-way threaded tree is called rightthreaded binary tree in two-way threaded treealso called double-threaded treethreads will appear in both the left and the right field of the node while the left field will point to the in-order predecessor of the nodethe right field will point to its successor two-way threaded binary tree is also called fully threaded binary tree one-way threading and two-way threading of binary trees are explained below figure shows binary tree without threading and its corresponding linked representation the in-order traversal of the tree is given as figure (alinked representation of the binary tree with one-way threading one-way threading figure shows binary tree with oneway threading and its corresponding linked representation node contains null pointer in its right fieldso it will be replaced to point to node which is its in-order successor similarlythe right field of node will point to node the right field of node will point to node the right field of node will point to node