申論題

4. (5%) Assume each node contains a data, Ithread, rthread, Icbild, and rchild fields. Ithread and rthread are Boolean fields. Icbild and rchild are pointers. If Ithread is true, the Ichild field will be considered as a left thread； otherwise, Ichild will point to the left child. Similarly for the rthread and rchild fields. Consider the following algorithm for pre-order traversal of a binary tree using thread pointers: