Other interesting recursive problems:

1) A "strictly binary tree" is a binary tree that has nonempty left and right substrees. Write a C function that accepts the root of a tree and returns true if the tree is strictly binary; otherwise, return false.

2) A "complete binary tree of depth d" is a strictly binary tree all of whose leafs are at level d. Write a recursive function that accepts the root of a tree and returns true if the tree is complete; otherwise, return false.

3) Write a recursive function to reverse the links of a singly linked list.