1. Linked List 1. Introduction to Linked List 2. Node Class 3. Linked List 4. The Bag Class with Linked List

2. Linked List Linked List Linked List Is a series of connected nodes, where each node is a data structure with data field and pointer(s) field. Is a series of connected nodes, where each node is a data structure with data field and pointer(s) field. Advantages over array implementation Advantages over array implementation Can grow and shrink in size, with no upper limit Can grow and shrink in size, with no upper limit Fast insertion and deletion Fast insertion and deletion Ω head

3. For this presentation, nodes in a linked list are objects, as shown here. data_field link_field 10 data_field link_field 15 data_field link_field 7 null class node { public: typedef double value_type;... private value_type data_field; node *link_field; }; Declarations for Linked Lists

4. typedef Keyword typedef int age_t; typedef int count_t; typedef double gpa_t; … age_t myAge = 21; count_t numElements = 5; gpa_t myGPA = 3.8; typedef int age_t; typedef int count_t; typedef double gpa_t; … age_t myAge = 21; count_t numElements = 5; gpa_t myGPA = 3.8; void someFunc(age_t age, count_t count); is clearer than void someFunct(int age, int count); void someFunc(age_t age, count_t count); is clearer than void someFunct(int age, int count);

5. Why Use typedef? Using typedefs can make your code clearer Using ypedefs can make your code easier to modify

6. The data_field of each node is a type called value_type, defined by a typedef. data_field link_field 10 data_field link_field 15 data_field link_field 7 null class node { public: typedef int value_type;... private value_type data_field; node *link_field; }; Declarations for Linked Lists

7. Each node also contains a link_field which is a pointer to another node. data_field link_field 10 data_field link_field 15 data_field link_field 7 null class node { public: typedef int value_type;... private value_type data_field; node *link_field; }; Declarations for Linked Lists

8. Your Turn Write the public interface for the Node classe.g, Constructors, accessors, modifiers. Write the public interface for the Node classe.g, Constructors, accessors, modifiers.

9. Solution class node{ public: //CONSTRUCTORS node(); node(const valueType& value, node* ptr); //CONSTANT FUNCTIONS valueType getData(); node* getNext(); //MODIFIER FUNCTIONS void setData(valueType newData); void setLink(node* newLink); private: valueType data; node* next; };

10. Declarations for Linked Lists A program can keep track of the front node by using a pointer variable such as head_ptr in this example. Notice that head_ptr is not a node -- it is a pointer to a node. head_ptr data_field link_field 10 data_field link_field 15 data_field link_field 7 null

11. Declarations for Linked Lists A program can keep track of the front node by using a pointer variable such as head_ptr. Notice that head_ptr is not a node -- it is a pointer to a node. We represent the empty list by storing null in the head pointer. head_ptr null

12. void list_head_insert(node*& head_ptr, const node::value_type& entry); Inserting a Node at the Front We want to add a new entry, 13, to the front of the linked list shown here. 10 15 7 null head_ptr entry 13

13. Inserting a Node at the Front Create a new node, pointed to by a local variable insert_ptr. 10 15 7 null head_ptr entry 13 insert_ptr void list_head_insert(node*& head_ptr, const node::value_type& entry);

14. Inserting a Node at the Front insert_ptr = new node; 10 15 7 null head_ptr entry 13 insert_ptr void list_head_insert(node*& head_ptr, const node::value_type& entry);

15. Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node; Place the data in the new node's data_field. void list_head_insert(node*& head_ptr, const node::value_type& entry);

16. Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node; Place the data in the new node's data_field. Connect the new node to the front of the list. void list_head_insert(node*& head_ptr, const node::value_type& entry);

17. Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node(entry, head_ptr); The correct new node can be completely created in one step by calling an appropriate node constructor. void list_head_insert(node*& head_ptr, const node::value_type& entry);

18. Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node(entry, head_ptr); Make the old head pointer point to the new node. void list_head_insert(node*& head_ptr, const node::value_type& entry);

19. Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; void list_head_insert(node*& head_ptr, const node::value_type& entry);

20. Inserting a Node at the Front insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; 10 15 7 null head_ptr 13 When the function returns, the linked list has a new node at the front. void list_head_insert(node*& head_ptr, const node::value_type& entry);

21. void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } Inserting a Node at the Front

22. void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } Does the function work correctly for the empty list ?

23. head_ptr entry 13 null Inserting a Node at the Front Does the function work correctly for the empty list ? void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; }

24. Inserting a Node at the Front head_ptr entry 13 null insert_ptr 13 void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } null

25. Inserting a Node at the Front head_ptr entry 13 insert_ptr 13 null void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; }

26. Inserting a Node at the Front head_ptr 13 null void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } When the function returns, the linked list has one node.

27. Caution! Always make sure that your linked list functions work correctly with an empty list.

28. Pseudocode for Inserting Nodes Nodes are often inserted at places other than the front of a linked list. There is a general pseudocode that you can follow for any insertion function...

29. Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry);

30. Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: Determine whether the new node will be the first node in the linked list. If so, then there is only one step: The function we already wrote list_head_insert(head_ptr, entry);

31. Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry); A pointer to the head of the list

32. Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry); The data to put in the new node

33. Pseudocode for Inserting Nodes Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position.

34. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. In this example, the new node will be the second node previous_ptr

35. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position What is the name of this orange pointer ? Look at the pointer which is in the node *previous_ptr previous_ptr

36. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position This pointer is called previous_ptr->link_field (although this name may be private to the node) What is the name of this orange pointer ? previous_ptr

37. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position previous_ptr->link_field points to the head of a small linked list, with 10 and 7 previous_ptr

38. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. The new node must be inserted at the front of this small linked list. 13 Write one C++ statement which will do the insertion. previous_ptr

39. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. 13 What might cause this statement to fail to compile? previous_ptr list_head_insert(previous_ptr->link_field, entry);

40. Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. 13 Use a node member function to get the link field if needed. previous_ptr list_head_insert(previous_ptr->link( ), entry);

41. Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry); Otherwise (if the new node will not be first): Set a pointer named previous_ptr to point to the node which is just before the new node's position. Make the function call: list_head_insert(previous_ptr->link( ), entry);

42. Pseudocode for Inserting Nodes The process of adding a new node in the middle of a list can also be incorporated as a separate function. This function is called list_insert in the linked list toolkit of Section 5.2. The process of adding a new node in the middle of a list can also be incorporated as a separate function. This function is called list_insert in the linked list toolkit of Section 5.2.

43. Pseudocode for Removing Nodes Nodes often need to be removed from a linked list. As with insertion, there is a technique for removing a node from the front of a list, and a technique for removing a node from elsewhere. Well look at the pseudocode for removing a node from the front of a linked list.

44. Removing the Head Node 10 15 7 null head_ptr 13 Start by setting up a temporary pointer named remove_ptr to the head node. remove_ptr

45. Removing the Head Node 10 15 7 null head_ptr 13 Set up remove_ptr. head_ptr = remove_ptr->link( ); remove_ptr Draw the change that this statement will make to the linked list.

46. Removing the Head Node 10 15 7 null head_ptr 13 Set up remove_ptr. head_ptr = remove_ptr->link( ); remove_ptr

47. Removing the Head Node Set up remove_ptr. head_ptr = remove_ptr->link( ); delete remove_ptr; // Return the node's memory to heap. 10 15 7 null head_ptr 13 remove_ptr

48. Removing the Head Node Heres what the linked list looks like after the removal finishes. 10 15 7 null head_ptr

49. It is easy to insert a node at the front of a list. The linked list toolkit also provides a function for inserting a new node elsewhere It is easy to remove a node at the front of a list. The linked list toolkit also provides a function for removing a node elsewhere--you should read about this function and the other functions of the toolkit. Summary

50. Doubly Linked List head Ω class node {... private: elementType data; node* next; node* previous; }; class list {... private: node* head; int count; }; Ω

51. insertAtFront() head Ω Ω newPtr Ω Ω head Ω newPtr Ω

52. insertAtFront() void list::insertAtFront(valueType item) { node* temp = new node(item, NULL, NULL); if (isEmpty()) head = temp; else { temp->setNext(head); head->setPrevious(temp); head = temp; } count++; }

53. removeFromFront() head Ω Ω Ω temp Ω Ω

54. removeFromFront() valueType list::removeFromFront() { valueType result = NIL; if (!isEmpty()) { result = head->getData(); node* temp = head; head->setPrevious(NULL); head = head->getNext(); delete temp; count--; } return result; }

55. insertAtBack() head Ω Ω newPtr Ω Ω head Ω newPtr Ω temp

56. insertAtBack() void list::insertAtBack(valueType item) { node* newPtr = new node(item, NULL, NULL); // find the last node if (isEmpty()) head = newPtr; else { node* temp = head; while (temp->getNext() != NULL) { temp = temp->getNext(); } temp->setNext(newPtr); newPtr->setPrevious(temp); } count++; }

57. removeFromBack() head Ω Ω Ω temp Ω Ω

58. removeFromBack() valueType list::removeFromBack() { valueType result = NIL; if (!isEmpty()) { // find last node node* temp = head; while (temp->getNext() != NULL) { temp = temp->getNext(); } // remove last node temp->getPrevious()->setNext(NULL); delete temp; } return result; }

59. Tail Pointer (to the last node) head Ω class node {... private: elementType data; node* next; }; class list {... private: node* head; node* tail; int count; }; tail