CS214 – Data Structures Lecture 8&9: Linked Lists

1. CS214 – Data StructuresLecture 8&9: Linked Lists Slides by Mohamed El-Ramly, PhD

2. Cairo University Faculty of Computers and Information Data Structures CS 214 2nd Term 2012-2013 Linked Lists

3. Readings Read Mark Weiss, Chap 3 http://www.youtube.com/watch?v=LOHBGyK3Hbs http://www.cosc.canterbury.ac.nz/mukundan/dsal/LinkListAppl.html Animated Data Structures http://www.ansatt.hig.no/frodeh/algmet/animate.html

4. Agenda Single Linked Lists Double Linked Lists Circular Linked Lists STL support for linked lists

5. Sites Learning a new language http://www.drdobbs.com/architecture-and-design/learning-new-languages/240150070 DrDobb’s Journal for Developers http://drdobbs.com/

6. 1- Linear Data Structures • Linear Data Structures (1 to 1) • Stacks • Queues • Linked Lists

7. 2- one-to-many Data Structures • Trees • Binary Search Tree Heap • B Tree and B+ Tree

8. 3- Many-to-many Data Structures • Graphs • Can represent numerous problems • Graph theory is an independent science that you can take PhD in. • Numerous algorithms were developed. • Think of 20 problems that can be represented as graphs.

9. 4- Non ordered Data Structures • Sets • Maps • Dictionaries • Hash Tables • (Items doe not have a particular order)

10. What is wrong with arrays? • ++ Fast access of data with indices • -- Size has to be known at compile time • -- Resizing needs re-location • -- Insertion and removal are O(n) • Data are continuous in memory • Data need to be shifted up or down

11. Single Linked Lists • Linked Lists avoid these problems by storing data in nodes that are linked by pointers. • Main operations: insert, delete, search • Better performance than arrays in some operations and worse perforamcne in others.

12. SLL Node Class class IntNode { int info; IntNode* next; public: IntNode () {next = 0;} IntNode (int n, IntNode* in = 0) { next = in; info = n; } IntNode* getNext () {return next;} void setNext(IntNode* pt) {next = pt;} int getInfo () {return info;} void setInfo (int n) {info = n;} };

13. Example SLL

14. Code to build the Previous SLL int main () { IntNode* p = new IntNode (10); p-> setNext (new IntNode (8)); p-> getNext() -> setNext (new IntNode (50)); for (IntNode* pt = p; pt != 0; pt = pt->getNext()) cout << *pt; system ("pause"); }

15. Code to build the Previous SLL friend ostream& operator<< (ostream& stream, IntNode node) { stream << node.getInfo(); stream << (node.getNext() == 0 ? "":"-> "); return stream; }

16. Chapter 10: Linked Lists

17. Chapter 10: Linked Lists

18. SLL Class class IntSLL { private: IntNode *head, *tail; public: IntSLL() {head = tail = NULL;} ~IntSLL (); void addToHead(int item); void addToTail(int item); void removeFromHead(); void removeFromTail(); friend ostream& operator<< (ostream& out, IntSLL list); };

19. SLL Operations • Insertion • at head • at tail • in the middle • Deletion • from head • from tail • from the middle • Search Chapter 10: Linked Lists

20. Head Insertion in SLL • Create newNode • newNode->setNext (head) • head = newNode • If (tail == null) • tail = head; • O(1) Chapter 10: Linked Lists

21. Head Insertion in SLL Chapter 10: Linked Lists

22. Tail Insertion in SLL • Create newNode • If (tail == null) • head = tail = newNode • Else • tail->setNext (newNode) • tail = newNode • O(1)

23. Tail Insertion in SLL Chapter 3: Linked Lists

25. Middle Insertion in SLL • Get ptr of item before location to insert in • If (location == 0) • Insert at Head • Else • Create newNode(item, ptr->getNext()) • ptr->setNext(newNode) • 4. If (tail == ptr) • tail = tail->getNext(); • O(n)

26. Middle Insertion in SLL • Create newNode • for (ptr = head; ptr != 0 && • count < index - 1; count++) • ptr = ptr->getNext(); • 4.if (ptr != 0 && !(index < 0)) • if (index == 0) • addToHead (item); • else • ptr->setNext(new IntNode • (item, ptr->getNext())); • 5. if (tail = ptr) • tail = tail->getNext(); • O(n)

27. Chapter 10: Linked Lists

28. Head Deletion in SLL • If head == tail// One node or nothing • head = tail = null • 2.Else • ptr = head • head = head -> getNext() • delete ptr • O(1) Chapter 10: Linked Lists

29. Head Deletion Code in SLL • IntNode* ptr = head; • if (head == tail) • head = tail = 0; • else { • head = head->getNext(); • delete ptr; • } • O(1) Chapter 10: Linked Lists

30. Head Deletion Code in SLL

31. Tail Deletion in SLL • If head == tail// One node or nothing • head = tail = null • 2.Else • get ptr to location before tail • delete tail • tail = ptr • tail-> setNext(null) • O(n) Chapter 10: Linked Lists

32. Tail Deletion Code in SLL • IntNode* ptr = head; • if (head == tail) • head = tail = 0; • else { • while (ptr->getNext() != tail) • ptr = ptr->getNext(); • delete tail; • tail = ptr; • tail->setNext(0); • } // O(n) Chapter 10: Linked Lists

33. Tail Deletion Code in SLL

34. Middle Deletion in SLL • Get item • If empty list • Return not found • 3.If item == head->getData() • Remove head • Retrun found • Else • Get ptr to nodewhose next • has the required item • If (ptr != null) • ptr->setNext (ptr->getNext()->getNext()) • Return found • Else Return not found • O(n)

35. Middle Deletion in SLL

37. Search in SLL • Get item • ptr = head • for(ptr != null && item not found) • ptr = ptr -> getNext() • 3.If ptr != null • return found • Else • return not found • O(n) Chapter 10: Linked Lists

38. Search in SLL bool search (int value){ IntNode* ptr = head; while (ptr != 0 && !(ptr->getInfo() == value)) ptr = ptr -> getNext(); return ptr != 0; } O(n) Chapter 10: Linked Lists

39. Chapter 10: Linked Lists

40. Double Linked Lists • Insert Head, remove head • Insert middle, remove middle • Insert Tail, remove tail • Write these algorithms yourself Chapter 10: Linked Lists

41. addToTail in Double Linked Lists Chapter 10: Linked Lists

42. removeFromTail in Double Linked Lists Chapter 10: Linked Lists

43. Circular Linked Lists • Read them from Adam Drozdek’s book, Chapter 3. Chapter 10: Linked Lists

44. Circular Linked Lists Chapter 10: Linked Lists

45. Chapter 10: Linked Lists

46. Chapter 10: Linked Lists

47. Self-Organizing Lists • Searching a Linked List is O(n) • Can we do better ? • Any ideas ? • We can, using one of these methods: • Move last accessed item to front method • Transpose method (swap towards head) • Order items by frequency of access • Keep the list sorted

48. Self-Organizing Lists

49. Chapter 10: Linked Lists

50. STL Support for LLs • STL implements a generic double linked list with head and tail pointers. • #include <list> (or list.h) • Has many interface functions: • void clear() • bool empty() • insert (iterator,T) • void push_back (T) • void sort() • void size()