CS 261. List Bag List Queue List Deque. by Tim Budd Ron Metoyer Sinisa Todorovic

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1 CS 261 List Bag List Queue List Deque by Tim Budd Ron Metoyer Sinisa Todorovic

2 List Bag struct { TYPE value; struct *; ; struct ListBag { struct *sentinel;

3 List Bag Init, Add operations are similar to List Stack Contains and Remove operations are tricky How to patch up links after removing an element?

4 Remove void removelistbag(struct ListBag *b, TYPE val) { val: 2 val: 7 val: 4 sentinel : : : null

5 Remove void removelistbag(struct ListBag *b, TYPE val) { struct *ious = b->sentinel; struct *current = b->sentinel->; while (current!= 0){ ious val: 2 current val: 7 val: 4 sentinel : : : null

= 0){ if (EQ(current->value,val)) { ious-> = current->; free(current); current

6 Remove void removelistbag(struct ListBag *b, TYPE val) { struct *ious = b->sentinel; struct *current = b->sentinel->; while (current!= 0){ if (EQ(current->value,val)) { ious-> = current->; free(current); current = ious->; else{ ious = current; current = current->; sentinel val: 2 : ious val: 7 : current val: 4 : null

7 When you find it When you find the element to be deleted, what does ious point to? What if the element to be deleted is at the front of the list? Does this matter?

8 List Queue Sentinel is a special link at the front and/or back of the list Has no value Never removed Simplifies some operations List front sentinel back

9 List Queue Add elements to the back of the list Remove elements from the front of the list Why not the other way around? List front Sentinel back

10 Implementation of ListQueue Worksheet 18

11 Structure for List Queue struct { TYPE value; struct * ; ; struct ListQueue { struct * head; struct * tail; ;

12 Init Makes the Sentinel void initlistqueue (struct ListQueue *q){ struct *sentinel = (struct *)malloc(sizeof(struct )); assert(sentinel!= 0); sentinel-> = 0; q->head = q->tail = sentinel; q tail head Sentinel

13 isempty int isemptylistqueue (struct ListQueue *q) { return q->head == q->tail;

14 Elements are Added to Tail void addbacklistqueue (struct ListQueue *q, TYPE val) { struct * lnk= (struct *) malloc(sizeof(struct )); assert(lnk!= 0); lnk-> = 0; lnk->value = val; q tail head Sentinel lnk

15 Add an Element (to Tail) void addbacklistqueue (struct ListQueue *q, TYPE val) { struct * lnk= (struct *) malloc(sizeof(struct )); assert(lnk!= 0); lnk-> = 0; lnk->value = val; q->tail-> = lnk; q tail head Sentinel lnk

16 Add void addbacklistqueue (struct ListQueue *q, TYPE val) { struct * lnk= (struct *) malloc(sizeof(struct )); assert(lnk!= 0); lnk-> = 0; lnk->value = val; q->tail-> = lnk; q->tail = lnk; tail q head Sentinel lnk

17 Remove (from Front) void removelistqueue (struct listqueue *q) { struct link * lnk = q->head->; q tail head Sentinel = lnk

18 Remove void removelistqueue (struct listqueue *q) { struct link * lnk = q->head->; assert (! isemptylistqueue(q)); q->head-> = lnk->; q head Sentinel tail = lnk

19 Remove void removelistqueue (struct listqueue *q) { struct link * lnk = q->head->; assert (! isemptylistqueue(q)); q->head-> = lnk->; if(q->head-> == 0) q->tail = q->head; free (lnk); q head Sentinel tail

20 Doubly ed Lists

21 Double s Allow access to both and ious link struct dlink { TYPE value; struct dlink * ; struct dlink * ious; ; val links val links links val

22 Deque Add/remove from both front and back Must maintain forward and backward links Deque head tail

23 If One Sentinel is Good Add a sentinel to BOTH front and back Eliminates the need to handle special cases Most "real" tools use two sentinels (e.g., Java) Deque backsentinel frontsentinel Sentinel Sentinel

24 Deque Interface int isempty(); void addfront(type val); /*Add value at front*/ void addback (TYPE val); /*Add value at back*/ void removefront(); void removeback (); TYPE front(); TYPE back(); /*Remove value at front*/ /*Remove value at back*/ /*Get value at front*/ /*Get value at back*/

25 Deque Structure struct dlink { TYPE value; ; struct dlink * ; struct dlink * ; struct listdeque { ; int size; struct dlink * frontsentinel; struct dlink * backsentinel;

26 initdeque void initdeque (struct listdeque *dq) { dq->frontsentinel = (struct dlink *) malloc(sizeof(struct dlink)); assert(dq->frontsentinel!= 0); dq->backsentinel = (struct dlink *) assert(dq->backsentinel!= 0); malloc(sizeof(struct dlink));...

27 initdeque void initdeque (struct listdeque *dq) { dq->frontsentinel = (struct dlink *) malloc(sizeof(struct dlink)); assert(dq->frontsentinel!= 0); dq->backsentinel = (struct dlink *) malloc(sizeof(struct dlink)); assert(dq->backsentinel!= 0); dq->frontsentinel-> = dq->backsentinel; dq->backsentinel-> = dq->frontsentinal; dq->size = 0;

28 Add to Front or Back void addfrontdeque (struct listdeque *dq, TYPE e) { _adddeque(dq, dq->frontsentinel->, e); void addbackdeque (struct listdeque *dq, TYPE e) { _adddeque(dq, dq->backsentinel, e);

29 Add Double to Deque void _adddeque (struct listdeque *dq, struct dlink *lnk, TYPE e){... What is *lnk? frontsentinel dq backsentinel

30 Add Double to Deque void _adddeque (struct listdeque *dq, struct dlink *lnk, TYPE e){ struct dlink * newlink = (struct dlink *) assert(newlink!= 0); newlink->value = e;... malloc(sizeof(struct dlink)); newlink frontsentinel dq lnk backsentinel

31 Add Double to Deque void _adddeque (struct listdeque *dq, frontsentinel struct dlink *lnk, TYPE e){ struct dlink * newlink = (struct dlink *) assert(newlink!= 0); newlink->value = e; newlink-> = lnk->; newlink-> = lnk; malloc(sizeof(struct dlink)); dq newlink If adding to front lnk backsentinel

32 Add Double to Deque void _adddeque (struct listdeque *dq, struct dlink *lnk, TYPE e){ struct dlink * newlink = (struct dlink *) assert(newlink!= 0); newlink->value = e; newlink-> = lnk->; newlink-> = lnk; lnk->-> = newlink; lnk-> = newlink; dq->size++; malloc(sizeof(struct dlink)); newlink lnk

Lesson 8: Linked List Deque

Lesson 8: Linked List Deque A linked list deque will combine features that we have examined in previous lessons. The deque will maintain a pointer to both the front and the back, use double links, and