worksheet 12: List Iterators Name:
An Active Learning Approach to Data Structures using C
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Worksheet 12: List Iterators
The careful reader might have noticed that we motivated the concept of a linked
list by saying insertions in the middle were more efficient than for a Vector, but
that subsequent lessons have only considered data structures in which elements
are added to the
end. The problem
is that without an
index it is difficult
to describe a
position in the
middle of a linked
list. One way to do
so is to use an
iterator. The
iterator interface has the definition shown at right. The combination of the
functions next and hasNext allows the user to write a loop that cycles over the
values in a collection. The remove method deletes the value most recently
returned as the current.
The LinkedList abstraction adds a pair of new functions. Through the execution of
these methods the user can modify the value held by a link, or add a new value
into the middle of a linked list. The newly added value will appear just before the
current element (or at the front of the list, if there is no current element).
Your task is to complete the implementation of the list iterator functions. These
build on the linked list abstraction you created in the previous lesson. Recall that
this list maintained sentinels at both the front and back, and used double links.
Be careful with the remove method. You want to make sure that when the next
iteration of the loop is performed the next element in sequence will be produced.
In order to solve this problem, remove must set the current element back to the
previous value before freeing its node. You can assume that the routines
listAddBefore and listRemoveLink that you wrote in an earlier lesson are
available.
struct listIterator {
struct list *list;
struct dlink *current;
};
/* prototypes for functions written in previous Lesson */
void listAddBefore (struct dlink *lnk, double d);
void listRemoveLink (struct dlink *lnk);
void listIteratorCreate (struct list *lst, struct listIterator
*litr);
int listIteratorHasNext (struct listIterator *litr);
EleType listIteratorCurrent (struct listIterator *litr);
void listIteratorRemove (struct listIterator *litr);
void listIteratorChange (struct listIterator *litr, EleType d);
void listIteratorAdd (struct listIterator *litr, EleType d);
