/**
 * The AVL node struct definition
 */
typedef struct avl_node_t avl_node_t;
struct avl_node_t {
	/* left child - smaller key */
	avl_node_t   *left;
	/* right child - bigger key */
	avl_node_t   *right;

	/* the key of the node which will also be used for sorting */
	char		*key;

	/* height of the node */
	int		height;
};

/**
 * The AVL tree struct definition
 */
typedef struct avl_tree_t avl_tree_t;
struct avl_tree_t {
	/* root of the tree */
	avl_node_t	*root;

	/* function used for sorting the keys */
	int	(*cmp)(const void *key1, const void *key2);
};