Linked Lists in Action

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1 Linked Lists in Action Chapter 5 introduces the oftenused data structure of linked lists. This presentation shows how to implement the most common operations on linked lists. CHAPTER 5 Data Structures and Other Objects

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

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

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

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

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

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

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

9 Inserting a Node at the Front void list_head_insert(node*&, const node::value_type& entry); insert_ptr = new node; insert_ptr entry 7

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

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

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

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

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

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

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

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

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

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

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

$Inserting a Node at the Front void list_head_insert(node*&, const node::value_type& entry) { node$

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

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

23 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...

24 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(, entry);

25 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(, entry);

26 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(, entry); A pointer to the head of the list

27 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(, entry);

28 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.

29 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. In this example, the new node will be the second node previous_ptr

30 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 Look at the pointer which is in the node *previous_ptr previous_ptr What is the name of this orange pointer? 7

31 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 This pointer is called previous_ptr->link_field (although this name may be private to the node) previous_ptr What is the name of this orange pointer? 7

32 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 previous_ptr->link_field points to the head of a small linked list, with 10 and 7 previous_ptr

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. The new node must be inserted at the front of this small linked list. previous_ptr Write one C++ statement which will do the insertion. 7

34 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. list_head_insert(previous_ptr->link_field, entry); previous_ptr What might cause this statement to fail to compile? 7

35 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. list_head_insert(previous_ptr->link( ), entry); previous_ptr Use a node member function to get the link field if needed. 7

36 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(, 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);

37 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.

38 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. We ll look at the pseudocode for removing a node from the front of a linked list.

39 Removing the Head Node Start by setting up a temporary pointer named remove_ptr to the head node. remove_ptr

40 Removing the Head Node Set up remove_ptr. = remove_ptr->link( ); Draw the change that this statement will make to the linked list. remove_ptr

41 Removing the Head Node Set up remove_ptr. = remove_ptr->link( ); remove_ptr

42 Removing the Head Node Set up remove_ptr. = remove_ptr->link( ); delete remove_ptr; // Return the node's memory to heap. remove_ptr

43 Removing the Head Node Here s what the linked list looks like after the removal finishes

44 Summary 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.

45 Presentation copyright 2010, Addison Wesley Longman, For use with Data Structures and Other Objects Using C++ by Michael Main and Walter Savitch. Some artwork in the presentation is used with permission from Presentation Task Force (copyright New Vision Technologies Inc) and Corel Gallery Clipart Catalog (copyright Corel Corporation, 3G Graphics Inc, Archive Arts, Cartesia Software, Image Club Graphics Inc, One Mile Up Inc, TechPool Studios, Totem Graphics Inc). Students and instructors who use Data Structures and Other Objects Using C++ are welcome to use this presentation however they see fit, so long as this copyright notice remains intact. THE END

Lecture 9 Linked Lists

CSC212 Data Structure - Section FG Lecture 9 Linked Lists Instructor: Feng HU Department of Computer Science City College of New York Motivation In a sequence using an array, inserting a new item needs