LINKED LISTS

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Chapter 17

• LINKED LISTS

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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

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Limitations

• Storing and processing data in an array has
  limitations
  
• Array size is fixed
• Only a fixed number of items can be stored in an
  array
  
• Searching for an item in an array is time
  consuming if data is not sorted
  
• If data is sorted, item insertion and deletion
  becomes time consuming

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Linked Lists

• A linked list is a collection of components,
  called nodes
  
• Every node (except the last node) contains the
  address of the next node
  
• Every node in a linked list has two components
• The address of the first node of the list is
  stored in a separate location, called head or
  first

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Linked Lists

• A list of items, called nodes, in which the order
  of the nodes is determined by the address, called
  the link, stored in each node

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Linked Lists

• The down arrow in the last node indicates that
  this link field is NULL
  
• The arrow in each node indicates that the address
  of the node to which it is pointing is stored in
  that node

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Linked List Properties

• This linked list has four nodes
• The address of the first node is stored in the
  pointer head
  
• Each node has two components a component, info,
  to store the info and another component, link, to
  store the address of the next node

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Linked List Navigation

• current head

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Linked List Navigation

• current current-link

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Insertion

• Consider the following linked list
• A new node with info 50 is to be created and
  inserted after p

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First Part of Insertion

• newNode new nodeType //create newNode
• newNode-info 50 //store 50 in the new node

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Tying New Node to List

• newNode-link p-link
• p-link newNode
• newNode-link p-link

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Completing the List

• p-link newNode

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Dangling List

• If we reverse the sequence of the statements,
  that is, suppose we execute the statements in the
  following order
  
• p-link newNode
• newNode-link p-link

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Simplifying Insertion

• The following two statements insert newNode
  between p and q
  
• newNode-link q
• p-link newNode
• Execution order does not matter

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Reversed Order

• If the statements are executed in the following
  order
  
• p-link newNode
• newNode-link q
• After the statement p-link newNode

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Completing an Insert

• newNode-link q

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Dangling Node Deletion

• Suppose the node with info 34 is to be deleted
  from the list

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Properly Deleting a Node

• After the statement p-link p-link-link
• The resulting figure is
• The node with info 34 is removed from the list
• The memory is still occupied by this node, that
  is, this node is dangling
  

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Properly Deleting a Node

• The following statements delete the node and
  deallocate the memory
  
• q p-link
• p-link q-link
• delete q
• After the statement q p-link

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Properly Deleting a Node

• After the statement p-link q-link the
  resulting figure is
  

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Properly Deleting a Node

• After the statement delete q the resulting
  figure is

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Deletion in the Link List ADT

• The basic operations on linked lists are
• 1. Initialize the list
• 2. Check if the list is empty
• 3. Check if the list is full
• 4. Search the list for a given item
• 5. Insert an item in the list
• 6. Delete an item from the list
• 7. Destroy the list
• 8. Print the list

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Deletion in the Link List ADT

• We also include the following operation on linked
  lists, which is helpful if we want to check the
  info of the first node
  
• 9. Retrieve the info contained in the first node

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Deletion in the Link List ADT

• 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
• After deletion, the list becomes empty.
  Therefore, after deletion, both first and last
  are set to NULL.

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Deletion in the Link List ADT

• Case 2 List is not empty
• The node to be deleted is the first node
• Consider the list of more than one node, as shown
  in Figure 17-28

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Deletion in the Link List ADT
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Deletion in the Link List ADT

• Case 3 Node to be deleted is not the first node,
  but is somewhere in this list
  
• Case 3a Node to be deleted is not the last node

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Deletion in the Link List ADT
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Deletion in the Link List ADT

• Case 3b Node to be deleted is the last node

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Insertion

• Case 1 The list is empty

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Insertion

• Case 2 The list is not empty, and the item to be
  inserted is smaller than the smallest item in the
  list

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Insertion

• Case 3 The list is not empty, and the item to be
  inserted is larger than the first item in the
  list
  
• Case 3a The item to be inserted is larger than
  the largest item in the list that is, it goes at
  the end of the list

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Insertion
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Insertion

• Case 3b The item to be inserted goes somewhere
  in the middle of the list

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Print List in Reverse Order

• Suppose that current is a pointer to a linked
  list
  
• if(current ! NULL)
• reversePrint(current-link) //print the
  tail
  
• coutinfonode
  
• Here the base case is hidden. The list is printed
  only if the pointer to the list is not NULL
  
• Inside the if statement the recursive call is on
  the tail of the list
  
• There are statements after the recursive call, so
  when the transfer comes back to the calling
  function, we must execute the remaining statements

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Doubly Linked Lists

• A doubly linked list is a linked list in which
  every node has a next and a back pointer
  
• A doubly linked list can be traversed in either
  direction. We can traverse the list starting at
  the first node or if a pointer to the last node
  is given, we can traverse the list starting at
  the last node

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Doubly Linked List Operations

• 1. Initialize the list
• 2. Destroy the list
• 3. Check whether the list is empty
• 4. Check whether the list is full
• 5. Search the list for a given item
• 6. Insert an item in the list
• 7. Delete an item from the list
• 8. Find the length of the list
• 9. Print the list

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insertNode

• Four cases
• 1. Insertion in an empty list
• 2. Insertion at the beginning of a nonempty list
• 3. Insertion at the end of a nonempty list
• 4. Insertion somewhere in a nonempty list

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Delete Node

• The delete operation has several cases
• 1. The list is empty
• 2. The item to be deleted is in the first node of
  the list, which would require us to change the
  value of the pointer first
  
• 3. The item to be deleted is somewhere in the
  list
  
• 4. The item to be deleted is not in the list

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Deletion Somewhere In List

• Case 3. Consider the list shown in Figure 17-47

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Deletion Somewhere In List
List after deleting 17 is shown in Figure 17-49
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Programming Example

• For a family or an individual, a favorite place
  to go on weekends or holidays is to a video store
  to rent movies
  
• A new video store in your neighborhood is about
  to open
  
• However, it does not have a program to keep track
  of its videos and customers
  
• The store managers want someone to write a
  program for their system so that the video store
  can function

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Programming Example

• The program should be able to perform the
  following operations
  
• 1. Rent a video that is, check out a video
• 2. Return, or check in, a video
• 3. Create a list of videos owned by the store
• 4. Show the details of a particular video
• 5. Print a list of all videos in the store
• 6. Check whether a particular video is in the
  store
  
• 7. Maintain a customer database
• 8. Print a list of all the videos rented by each
  customer

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Programming Example

• From the programming requirement, we see that
  there are two major components of the video
  store
  
• a video
• a customer
• Also, we need to maintain three lists
• 1. A list of all videos in the store
• 2. A list of all customers of the store
• 3. A list of rented videos

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Part 1 The Video Component

• The common things associated with a video are
• 1. Name of the movie
• 2. Names of the stars
• 3. Name of the producer
• 4. Name of the director
• 5. Name of the production company
• 6. Number of copies in store

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Video List

• This program requires us to maintain a list of
  all videos in the store, and we should be able to
  add a new video to our list
  
• We use a linked list to create a list of videos

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Video List
The node of a video list has the form shown in
Figure 17-54
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Part 2 Customer Component

• The customer object stores information about a
  customer, such as first name, last name, account
  number, and a list of videos rented by the
  customer
• Thus, our video store program has two
  components
  
• 1. A video object that contains the necessary
  information about a video as described
  previously
  
• 2. A customer object that contains the necessary
  information about a customer, which will be
  described soon

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Part 2 Customer Component

• We will create two lists that correspond to these
  two objects
  
• a. A list of all videos in the store (as
  described earlier)
  
• b. A list of all customers

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Part 2 Customer Component

• The primary characteristics of a customer are
• 1. The customers first name
• 2. The customers last name
• 3. The customers account number
• 4. The list of rented videos

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Basic Operations

• The basic operations on an object of the type
  personType are
  
• 1. Print the name
• 2. Set the name
• 3. Show the first name
• 4. Show the last name

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Basic Operations

• The basic operations on an object of the type
  customerType are
  
• 1. Print the name, account number, and number of
  rentals
  
• 2. Set the name, account number, and number of
  rentals
  
• 3. Rent a video, add video to the list of rented
  video list
  
• 4. Return a video, delete video from the list of
  rented video list
  
• 5. Show account number

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Main Program

• The data in the input file is in the form
• video title (that is, name of the movie)
• movie star1
• movie star2
• movie producer
• movie director
• movie production co.
• number of copies
• .
• .
• .

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Algorithm of the Main Function

• 1. Open the input file, if input file does not
  exist, exit the program
  
• 2. Create the list of videoscreateVideoList
• 3. Show the menudisplayMenu
• 4. While not done, perform various operations

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CreateVideoList

• a. Read the data and store it in a video object
• b. Insert the video in the list
• c. Repeat steps a and b for each videos data in
  the file

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displayMenu

• a. Select one of the following
• b. 1 To check whether a particular video is in
  the store
  
• c. 2 To check out a video
• d. 3 To check in a video
• e. 4 To check whether a particular video is in
  the store
  
• f. 5 To print the titles of all videos
• g. 6 To print a list of all videos
• h. 9 To exit