1 / 123

CH4. LINKED LISTS

CH4. LINKED LISTS. 4.1 Singly Linked Lists. Sequential representation successive nodes of the data object are stored a fixed distance apart order of elements is the same as in ordered list adequate for functions such as accessing an arbitrary node in a table

asifuentes
Télécharger la présentation

CH4. LINKED LISTS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CH4. LINKED LISTS

  2. 4.1 Singly Linked Lists • Sequential representation • successive nodes of the data object are stored a fixed distance apart • order of elements is the same as in ordered list • adequate for functions such as accessing an arbitrary node in a table • operations such as insertion and deletion of arbitrary elements from ordered lists become expensive • Linked representation • successive items of a list may be placed anywhere in memory • order of elements need not be the same as order in list • each data item is associated with a pointer (link) to the next item

  3. 4.1 Singly Linked Lists(Cont’) • List of 3-letter words : (BAT, CAT, EAT, ..., VAT, WAT) data[8] = BAT first = 8 link[8] = 3 data[3] = CAT Figure 4.1: Nonsequential list representation

  4. 4.1 Singly Linked Lists(Cont’) first BAT CAT EAT WAT 0 Figure 4.2 : Usual way to draw a linked list

  5. 4.1 Singly Linked Lists(Cont’) • To insert GAT between FAT and HAT (1) get a node N that is currently unused ; let its address be x (2) set the data field of N to GAT (3) set the link field of N to point to the node after FAT, which contains HAT (4) set the link field of the node containing FAT to x

  6. 4.1 Singly Linked Lists(Cont’) Figure 4.3 : Inserting a node

  7. 4.1 Singly Linked Lists(Cont’) • To delete GAT • find the element that immediately precedes GAT, which is FAT • set the link field of FAT to the position of HAT first BAT CAT EAT FAT GAT HAT WAT 0 Figure 4.4 : Delete GAT from list Note : must know the previous element

  8. 4.2 Representing Lists in C++ 4.2.1 Defining A List Node in C++ • Defining a List Node in C++ • Class definition for 3-letter node • A more complicated list structure class ThreeLetterNode{private: char data[3]; ThreeLetterNode *link; }; class nodea{ private: int data1; char data2; float data3; nodea *linka; nodeb *linkb; }; class nodeb{ private: int data; nodeb *link; };

  9. 4.2 Representing Lists in C++(Cont’) 22 data data1 5.5 link data2 ‘c’ data3 3.14 linka linkb nodeb nodea Figure 4.5 : Illustration of the node structures nodea and nodeb

  10. 4.2 Representing Lists in C++(Cont’) 4.2.2 Designing a list in C++ • Design approach • use a class ThreeLetterList corresponding to the entire list data structure • ThreeLetterList supports member functions for list manipulation operations • use a composite of two classes, ThreeLetterNode and ThreeLetterList • ThreeLetterList HAS-A ThreeLetterNode • Definition • a data object of type A HAS-A data object of type B if A conceptually contains B

  11. 4.2 Representing Lists in C++(Cont’) Figure 4.6 : Referencing the data members of a node

  12. 4.2 Representing Lists in C++(Cont’) ThreeLetter List ThreeLetter Node first CAT EAT WAT 0 Figure 4.7 : Conceptual relationship between ThreeLetterList and ThreeLetterNode

  13. 4.2 Representing Lists in C++(Cont’) • ThreeLetterList • contains only the pointer first • declare to be a friend of ThreeLetterNode • only member functions of ThreeLetterList and ThreeLetterNode can access the private members of ThreeLetterNode • only list manipulation operations have access to data members of ThreeLetterNode ThreeLetter List ThreeLetter Node first BAT CAT WAT 0 Figure 4.8 : Actual relationship between ThreeLetterList and ThreeLetterNode

  14. 4.2 Representing Lists in C++(Cont’) class ThreeLetterList; // forward declaration class ThreeLetterNode{friend class ThreeLetterList;private: char data[3]; ThreeLetterNode *link;}; class ThreeLetterList{public: // List Manipulation operations…private: ThreeLetterNode *first;}; Program 4.1 : Composite classes

  15. 4.2 Representing Lists in C++(Cont’) • Nested Classes • one class is defined inside the definition of another class • ThreeLetterNode objects (private) cannot be accessed outside class ThreeLetterList • ThreeLetterNode data members are public, so they can be accessed by member functions of ThreeLetterList

  16. 4.2 Representing Lists in C++(Cont’) class ThreeLetterList{public: // List Manipulation operations…. private: class ThreeLetterNode{ // nested class public: char data[3]; ThreeLetterNode *link; }; ThreeLetterNode *first;}; Program 4.2 : Nested classes

  17. 4.2 Representing Lists in C++(Cont’) • Using composite classes, the node class can be used by two data structures

  18. 4.2 Representing Lists in C++(Cont’) 4.2.3 Pointer Manipulation in C++ • new command • delete command • null command • ThreeLetterNode* f; • nodea* y; • nodeb* z; • f = new ThreeLetterNode; • y = new nodea; • z = new nodeb; • *f : the node of type ThreeLetterNode delete f; delete y; delete z; constant 0

  19. 4.2 Representing Lists in C++(Cont’) x a a b x y b b b y (a) (b) x=y (c) *x=*y Figure 4.9 : Effect of pointer assignments

  20. 4.2 Representing Lists in C++(Cont’) 4.2.4 List Manipulation Operations class List {private: ListNode *first;public: .... }; class ListNode {friend class List;private: int data; ListNode *link; };

  21. 4.2 Representing Lists in C++(Cont’) void List::Create2(){ first = new ListNode(10); // create and initialize first node // create and initialize second node and place its address in first→link first→link = new ListNode(20);} ListNode::ListNode(int element = 0) // 0 is the default argument // in constructor for List Node{ data = element; link = 0; // null pointer constant} Program 4.3 : Creating a two-node list

  22. 4.2 Representing Lists in C++(Cont’) first 10 20 0 Figure 4.10 : A two-node list

  23. 4.2 Representing Lists in C++(Cont’) • Example void List::Insert50(ListNode *x) { //insert new node after x ListNode *t = new ListNode(50); //create and initialize new node if(!first) //insert into empty list { first = t; return; //exit List::Insert50 } //insert after x t->link = x->link; x->link = t;} Program 4.4 : Inserting a node

  24. 4.2 Representing Lists in C++(Cont’) first first x 50 0 0 t t 50 (a) (b) Figure 4.11 : Inserting into an empty and nonempty list

  25. 4.2 Representing Lists in C++(Cont’) Void List::Delete(ListNode *x, ListNode *y){ // delete x placed after y if(!y) first = first->link; else y->link = x->link; delete x; // return the node} Program 4.5 : Deleting a node x first y x first

  26. 4.2 Representing Lists in C++(Cont’) Figure 4.12 : Possible configuration for a singly linked list traversed in both directions

  27. 4.3 A Reusable Linked List Class 4.3.1 Implementing Linked Lists with Templates • Implementing Linked Lists with Templates • Linked-list • a container class • good for implementation with templates • an empty linked list of integers intlist List<int> intlist;

  28. 4.3 A Reusable Linked List Class(Cont’) template <class Type> class List; // forward declaration template <class Type>class ListNode{ friend class List<Type>;private: Type data; ListNode *link;}; template <class Type>class List{public: List() first = 0;; // constructor initializing first to 0 // List manipulation operations…. private: ListNode<Type> *first;}; Program 4.6 : Template definition of linked lists

  29. 4.3 A Reusable Linked List Class(Cont’) 4.3.2 Linked Lists Iterators • Iterator • an object that is used to traverse all the elements of a container class • Example operations on an integer container class C • print all integers in C • obtain the max, min, mean, median, or mode of all integers in C • obtain the sum or product of all integers in C • Pseudo-code for the operations initialization step;for each item in C { current=current item of C; body;}postprocessing step;

  30. 4.3 A Reusable Linked List Class(Cont’) int x = -MAXINT; // initialization statement for each item in C { current = current item of C; x = max(current, x); // body } return x; // postprocessing step Program 4.7 : Pseudo-code for computing maximum element

  31. 4.3 A Reusable Linked List Class(Cont’) • All operations have to be implemented as member functions of a particular container class • drawbacks • many operations do not make sense to certain object types • too many operations in a class • users have to learn how to traverse the container class • ListIterator<Type> • handles details of the linked list traversal • retrieves elements stored in the list

  32. 4.3 A Reusable Linked List Class(Cont’) enum Boolean { FALSE, TRUE};template <class Type> class List;template <class Type> class ListIterator; template <class Type> class ListNode{ friend class List<Type>; friend class ListIterator<Type>;private: Type data; ListNode *link;}; template <class Type> class List{ friend class ListIterator<Type>;public: List() {first = 0;}; // List manipulation operations … private: ListNode<Type> *first; }; list first

  33. 4.3 A Reusable Linked List Class(Cont’) template <class Type> class ListIterator{ public: ListIterator(const List<Type> &l): list(l), current(l.first) {}; Boolean NotNull(); Boolean NextNotNull(); Type* First(); Type* Next(); private: const List<Type> &list; // refers to an existing list ListNode<Type> *current; // points to a node in list }; Program 4.8 : Template definition of linked lists

  34. 4.3 A Reusable Linked List Class(Cont’) template <class Type> // check that the current element in list is non-null Boolean ListIterator<Type>::NotNull(){ if(current) return TRUE; else return FALSE;} template <class Type> //check that the next element in list is non-null Boolean ListIterator<Type>::NextNotNull(){ if(current && current->link) return TRUE; else return FALSE;}

  35. 4.3 A Reusable Linked List Class(Cont’) template <class Type> // return a pointer to the first element of listType* ListIterator<Type>::First(){ if(list.first) return &list.first->data; else return 0;} template <class Type> // return a pointer to the next element of listType* ListIterator<Type>::Next(){ if(current){ current = current->link; if (current) return &current->data; } else return 0;} Program 4.9 : List iterator functions

  36. 4.3 A Reusable Linked List Class(Cont’) int sum(const List<int>& l){ Listiterator<int> li(l); // li is associated with list l if(!li.NotNull()) return 0; // empty list, return 0 int retvalue = *li.First(); // get first element while(li.NextNotNull()) // make sure that next element exists retvalue += *li.Next(); // get it, add it to the current total return retvalue; } Program 4.10 : Using iterators to compute the sum of elements

  37. 4.3 A Reusable Linked List Class(Cont’) • Function sum does not require access to the private data members of List<Type> or List node<Type> Listlterator current List List ListNode first

  38. 4.3 A Reusable Linked List Class(Cont’) 4.3.3 Linked List Operations • Operations included in most reusable classes • constructors (including default and copy constructors) • a destructor • operator= • operator== • operators to input and output a class object (by overloading operator>> and operator<<) • Operations in a linked list class • insertion, deletion, other manipulations • last : a private data member in List<Type>

  39. 4.3 A Reusable Linked List Class(Cont’) template<class Type> void List<Type>::Attach(Type k){ ListNode<Type>* newnode = new ListNode<Type>(k); if ( first==0 ) first = last = newnode; else { last->link = newnode; last = newnode; } } Program 4.11 : Attaching a node to the end of a list

  40. 4.3 A Reusable Linked List Class(Cont’) template <class Type>void List<Type>::Invert() // A chain x is inverted so that if x = (a1, ..., an), // then, after execution, x = (an, ..., a1).{ ListNode<Type> *p = first, *q = 0; // q trails p while(p){ ListNode<Type> *r = q; q = p; // r trails q p = p->link; // p moves to next node q->link = r; // link q to preceding node } first = q;} Program 4.12 : Inverting a list

  41. 4.3 A Reusable Linked List Class(Cont’) 1 st iteration q p 2 nd iteration r q p

  42. 4.3 A Reusable Linked List Class(Cont’) template <class Type> void List<Type>::Concatenate(List<Type>b) // this = (a1, ..., am) and b = (b1, ..., bn), m, n≥0 // produces the new chain z = (a1, ..., am, b1, ..., bn) in this. { if (!first) { first = b.first; return; } if (b.first) { for (ListNode<Type> *p = first; p->link; p = p->link); // no body p->link = b.first; } } Program 4.13 : Concatenating two chains

  43. 4.4 Circular Lists • Circular list • link field of the last node points to the first node in the list • to check whether current points to the last node: current→link==first first BAT CAT WAT EAT Figure 4.13 : A circular list

  44. 4.4 Circular Lists(Cont’) first x1 x2 x3 Data link Figure 4.14 : Example of a circular list last x1 x2 x3 Data link Figure 4.15 : Pointing to the last node of a circular list

  45. 4.4 Circular Lists(Cont’) template <class Type> void CircList::InsertFront(ListNode <Type> *x) // Insert the node pointed at by x at the "front" of the circular // list this, where last points to the last node in the list. { if(!last){ // empty list last = x; x->link = x; } else { x->link = last->link; last->link = x; } } Program 4.14 : Inserting at the front

  46. 4.4 Circular Lists(Cont’) • last : the private data member that points to the last node • a dummy head node : to avoid a case in which the empty list is handled specially first (a) first BAT CAT EAT WAT (b) Figure 4.16 : A circular list with a head node

  47. 4.5 Linked Stacks and Queues Figure 4.17 : Linked stack and queue

  48. 4.5 Linked Stacks and Queues(Cont’) class Stack; // forward declaration class StackNode { friend class Stack; private: int data; StackNode *link; StackNode(int d=0, StackNode *l=0): data(d), link(l) {}; // condtructor }; class Stack { public: Stack() {top=0;}; // constructor void Add(condt int); int* Delete(int&); private: StackNode *top; void StackEmpty(); }; Program 4.15 : Stack class definition

  49. 4.5 Linked Stacks and Queues(Cont’) void Stack :: Add(const int y){ top = new stackNode(y, top); } Program 4.16 : Adding to a linked stack int* Stack :: Delete(int& retvalue) // delete top node from stack and return a pointer to its data { if (top==0){StackEmpty(); return 0;}// return null pointer constant StackNode *delnode = top; retvalue=top->data; // get data field of top node top=top->link; // remove top node delete delnode; // free the node return &retvalue; // return pointer to data } Program 4.17 : Deleting from a linked stack

  50. 4.5 Linked Stacks and Queues(Cont’) void Queue :: Add(const int y) { if (front==0) front = rear = new QueueNode(y, 0); // empty queue else rear = rear->link = new QueueNode(y, 0); // attach node and update rear } Program 4.18 : Adding to a linked queue int* Queue :: Delete(int& retvalue) // delete top node in queue and return a pointer to its data { if (top==0){QueueEmpty(); return 0;} QueueNode *x = front; retvalue=front->data; // get data front=x->link; // delete front node delete x; // free the node return &retvalue; // return pointer to data } Program 4.19 : Deleting from a linked queue

More Related