Download Chapter 17-1

C++ Programming:
Program Design Including
Data Structures, Fourth Edition
Chapter 17: Linked Lists
Objectives
In this chapter, you will:
• Learn about linked lists
• Become aware of the basic properties of
linked lists
• Explore the insertion and deletion operations
on linked lists
• Discover how to build and manipulate a
linked list
• Learn how to construct a doubly linked list
C++ Programming: Program Design Including Data Structures, Fourth Edition
2
Introduction
• Data can be organized and processed
sequentially using an array, called a
sequential list
• Problems with an array
− Array size is fixed
− Unsorted array: searching for an item is slow
− Sorted array: insertion and deletion is slow
C++ Programming: Program Design Including Data Structures, Fourth Edition
3
Linked Lists
• Linked list: a list of items (nodes), in which the
order of the nodes is determined by the
address, called the link, stored in each node
Link field in last node
is NULL
C++ Programming: Program Design Including Data Structures, Fourth Edition
4
Linked Lists (continued)
• Example:
− Suppose that the first node is at memory
location 1200, and the second node is at
memory location 1575
C++ Programming: Program Design Including Data Structures, Fourth Edition
5
Linked Lists (continued)
• Because each node of a linked list has two
components, we need to declare each node
as a class or struct
− Data type of a node depends on the specific
application
− The link component of each node is a pointer
C++ Programming: Program Design Including Data Structures, Fourth Edition
6
Linked Lists: Some Properties
C++ Programming: Program Design Including Data Structures, Fourth Edition
7
Linked Lists: Some Properties
(continued)
• current = head;
− Copies value of head into current
C++ Programming: Program Design Including Data Structures, Fourth Edition
8
Linked Lists: Some Properties
(continued)
• current = current->link;
C++ Programming: Program Design Including Data Structures, Fourth Edition
9
Linked Lists: Some Properties
(continued)
C++ Programming: Program Design Including Data Structures, Fourth Edition
10
Traversing a Linked List
• The basic operations of a linked list are:
− Search to determine if an item is in the list
− Insert an item in the list
− Delete an item from the list
• Traversal: given a pointer to the first node of
the list, step through the nodes of the list
C++ Programming: Program Design Including Data Structures, Fourth Edition
11
Traversing a Linked List
(continued)
• To traverse a linked list:
• Example:
C++ Programming: Program Design Including Data Structures, Fourth Edition
12
Item Insertion and Deletion
• Consider the following definition of a node:
• We will use the following variable declaration:
C++ Programming: Program Design Including Data Structures, Fourth Edition
13
Insertion
• Consider the following linked list:
• A new node with info 50 is to be created
and inserted after p
C++ Programming: Program Design Including Data Structures, Fourth Edition
14
The sequence of statements to insert the node is very important. Suppose
that we reverse the sequence of the statements and execute the
statements in the following order:
Insertion (continued)
• Using two pointers, we can simplify the
insertion code somewhat
• To insert newNode between p and q:
The order in which these statements
execute does not matter
C++ Programming: Program Design Including Data Structures, Fourth Edition
17
Deletion
Node with info 34 is removed from the list, but
memory is still occupied; node is dangling
C++ Programming: Program Design Including Data Structures, Fourth Edition
19
Building a Linked List
• If data is unsorted
− The list will be unsorted
• Can build a linked list forward or backward
− Forward: a new node is always inserted at the
end of the linked list
− Backward: a new node is always inserted at
the beginning of the list
C++ Programming: Program Design Including Data Structures, Fourth Edition
21
Building a Linked List Forward
• You need three pointers to build the list:
− One to point to the first node in the list, which
cannot be moved
− One to point to the last node in the list
− One to create the new node
C++ Programming: Program Design Including Data Structures, Fourth Edition
22
Building a Linked List Forward
(continued)
We now repeat statements 1 through 6b three more times:
C++ Programming: Program Design Including Data Structures, Fourth Edition
25
Building a Linked List Backward
• The algorithm is:
− Initialize first to NULL
− For each item in the list
•
•
•
•
Create the new node, newNode
Store the item in newNode
Insert newNode before first
Update the value of the pointer first
C++ Programming: Program Design Including Data Structures, Fourth Edition
27
Linked List as an ADT
• The basic operations on linked lists are:
− Initialize the list
− Determine whether the list is empty
− Print the list
− Find the length of the list
− Destroy the list
C++ Programming: Program Design Including Data Structures, Fourth Edition
29
Linked List as an ADT (continued)
• The basic operations on linked lists are:
(continued)
− Retrieve the info contained in the first node
− Retrieve the info contained in the last node
− Search the list for a given item
− Insert an item in the list
− Delete an item from the list
− Make a copy of the linked list
C++ Programming: Program Design Including Data Structures, Fourth Edition
30
Linked List as an ADT (continued)
• In general, there are two types of linked lists:
− Sorted and unsorted lists
• The algorithms to implement the operations
search, insert, and remove slightly differ for
sorted and unsorted lists
• abstract class linkedListType will
implement the basic linked list operations
− Derived classes: unorderedLinkedList
and orderedLinkedList
C++ Programming: Program Design Including Data Structures, Fourth Edition
31
Linked List as an ADT (continued)
• If a linked list is unordered, we can insert a
new item at either the end or the beginning
− buildListForward inserts item at the end
− buildListBackward inserts new item at the
beginning
• To accommodate both operations, we will
write two functions:
− insertFirst and insertLast
• We will use two pointers in the list:
− first and last
C++ Programming: Program Design Including Data Structures, Fourth Edition
32
Structure of Linked List Nodes
• The node has two member variables
• To simplify operations such as insert and
delete, we define the class to implement the
node of a linked list as a struct
• The definition of the struct nodeType is:
C++ Programming: Program Design Including Data Structures, Fourth Edition
33
Member Variables of the class
linkedListType
• We use two pointers: first and last
• We also keep a count of the number of
nodes in the list
• linkedListType has three member
variables:
C++ Programming: Program Design Including Data Structures, Fourth Edition
34
Linked List Iterators
• One of the basic operations performed on a
list is to process each node of the list
− List must be traversed, starting at first node
− Common technique is to provide an iterator
• Iterator: object that produces each element of
a container, one element at a time
− The two most common operations are:
++ (the increment operator)
* (the dereferencing operator)
C++ Programming: Program Design Including Data Structures, Fourth Edition
35
Linked List Iterators (continued)
• Note that an iterator is an object
• We need to define a class
(linkedListIterator) to create iterators
to objects of the class linkedListType
− Would have two member variables:
• One to refer to (the current) node
• One to refer to the node just before the (current)
node
C++ Programming: Program Design Including Data Structures, Fourth Edition
36
Linked List Iterators (continued)
C++ Programming: Program Design Including Data Structures, Fourth Edition
38
Print the List
C++ Programming: Program Design Including Data Structures, Fourth Edition
45
Length of a List
C++ Programming: Program Design Including Data Structures, Fourth Edition
46
Retrieve the Data of the First Node
C++ Programming: Program Design Including Data Structures, Fourth Edition
47
Retrieve the Data of the Last Node
C++ Programming: Program Design Including Data Structures, Fourth Edition
48
Begin and End
C++ Programming: Program Design Including Data Structures, Fourth Edition
49
Copy the List
• Steps:
− Create a node, and call it newNode
− Copy the info of the node (in the original list)
into newNode
− Insert newNode at the end of the list being
created
C++ Programming: Program Design Including Data Structures, Fourth Edition
50
Destructor
C++ Programming: Program Design Including Data Structures, Fourth Edition
53
Copy Constructor
C++ Programming: Program Design Including Data Structures, Fourth Edition
54
Overloading the Assignment
Operator
C++ Programming: Program Design Including Data Structures, Fourth Edition
55
Unordered Linked Lists
• We derive the class
unorderedLinkedList from the abstract
class linkedListType and implement
the operations search, insertFirst,
insertLast, and deleteNode
C++ Programming: Program Design Including Data Structures, Fourth Edition
56
Unordered Linked Lists
(continued)
C++ Programming: Program Design Including Data Structures, Fourth Edition
58
Search the List
• Steps:
− Compare the search item with the current
node in the list
• If the info of the current node is the same as the
search item, stop the search
• Otherwise, make the next node the current node
− Repeat Step 1 until the item is found
• Or, until no more data is left in the list to compare
with the search item
C++ Programming: Program Design Including Data Structures, Fourth Edition
59
Insert the First Node
• Steps:
− Create a new node
− Store the new item in the new node
− Insert the node before first
− Increment count by 1
C++ Programming: Program Design Including Data Structures, Fourth Edition
61
Insert the Last Node
C++ Programming: Program Design Including Data Structures, Fourth Edition
63
Delete a Node
• Case 1: List is empty
− If the list is empty, output an error message
• Case 2: List is not empty
− The node to be deleted is the first node
− First scenario: List has only one node
C++ Programming: Program Design Including Data Structures, Fourth Edition
64
Delete a Node (continued)
− Second scenario: List of more than one node
C++ Programming: Program Design Including Data Structures, Fourth Edition
65
Delete a Node (continued)
• Case 3: Node to be deleted is not the first one
− Case 3a: Node to be deleted is not last one
C++ Programming: Program Design Including Data Structures, Fourth Edition
66
Delete a Node (continued)
− Case 3b: Node to be deleted is the last node
C++ Programming: Program Design Including Data Structures, Fourth Edition
67
Delete a Node (continued)
• Case 4: Node to be deleted is not in the list
− The list requires no adjustment
− Simply output an error message
C++ Programming: Program Design Including Data Structures, Fourth Edition
68
Header File of the Unordered
Linked List
C++ Programming: Program Design Including Data Structures, Fourth Edition
71
Header File of the Unordered
Linked List (continued)
C++ Programming: Program Design Including Data Structures, Fourth Edition
72
Ordered Linked Lists
• (This topic continues in file
02225_PPT_ch17-2.ppt)
C++ Programming: Program Design Including Data Structures, Fourth Edition
73