The null left pointer pointing to predecessor and null right pointer pointing to successor. how many types of threaded tree are possible with this convention?

A threaded tree is a binary tree where null pointers of certain nodes are made to point to their predecessor or successor, effectively allowing in-order traversal without recursion or a stack. With regards to the conventions you mentioned (null left pointer pointing to the predecessor and null right pointer pointing to the successor), we can classify the types of threaded trees as follows:

1. Single Threaded Tree: In this type, only one of the pointers (left or right) is made to point to the predecessor or successor.

   • Left-Threaded Tree: Here, only the null left pointers point to the predecessor.
   • Right-Threaded Tree: In this case, only the null right pointers point to the successor.

2. Double Threaded Tree: In a double threaded tree, both the null left and right pointers are utilized to point to the predecessor and the successor, respectively.

Given this classification, we can conclude that there are three types of threaded tree possible with the convention you specified:

1. Left-Threaded Tree
2. Right-Threaded Tree
3. Double Threaded Tree

In total, three types of threaded trees can be constructed under the given conventions.