/*
 * Simple tree node representation
  */
struct node_t {
  struct node_t *left;
  struct note_t *right;
};

/*
 * Return the maximum depth of the tree given a pointer
 * to its root node.
 */
unsigned int
tree_depth (node_t *root)
{
   return (NULL == root) ? 0 :
           MAX(tree_depth(root->left, root->right)+1);
}