Lesson 5 link list

Lesson 5 – Linked List
4/4/2021 PC-108 DATA STRUCTURE AND ALGORITHM BY: AREGATON

A Simple Linked List
Our first example program, linkList.java,
demonstrates a simple linked list. The only
operations allowed in this version of a list
are:
 Inserting an item at the beginning of the list
 Deleting the item at the beginning of the list
 Iterating through the list to display its contents
4/4/2021 PC-108 DATA STRUCTURE AND ALGORITHM 2
The Link Class
You’ve already seen the data part of the Link
class. Here’s the complete class definition:

The linkList.java Program
Listing 5.1 shows the complete linkList.java program. You’ve already seen all the components
except the main() routine.

The linkList.java Program

Output:
In main() we create a new list, insert four new links into it with insertFirst(), and display it. Then,
in the while loop, we remove the items one by one with deleteFirst() until the list is empty. The
empty list is then displayed. Here’s the output from linkList.java:
List (first-->last): {88, 8.99} {66, 6.99} {44, 4.99} {22, 2.99}
Deleted {88, 8.99}
Deleted {66, 6.99}
Deleted {44, 4.99}
Deleted {22, 2.99}
List (first-->last):

Finding and Deleting Specified Links
Our next example program adds methods to
search a linked list for a data item with a specified
key value and to delete an item with a specified
key value. These, along with insertion at the start
of the list, are the same operations carried out by
the LinkList Workshop applet. The complete
linkList2.java program is shown in Listing 5.2.

Output:
The main() routine makes a list, inserts four items, and displays the resulting list. It then
searches for the item with key 44, deletes the item with key 66, and displays the list again.
Here’s the output:
List (first-->last): {88, 8.99} {66, 6.99} {44, 4.99} {22, 2.99}
Found link with key 44
Deleted link with key 66
List (first-->last): {88, 8.99} {44, 4.99} {22, 2.99}

LISTING 5.3 The firstLastList.java Program

For simplicity, in this program we’ve reduced the number of
data items in each link from two to one. This makes it easier to
display the link contents. (Remember that in a serious program
there would be many more data items, or a reference to
another object containing many data items.) This program
inserts three items at the front of the list, inserts three more at
the end, and displays the resulting list. It then deletes the first
two items and displays the list again.
List (first-->last): 66 44 22 11 33 55
List (first-->last): 22 11 33 55

LISTING 5.4 The linkStack.java Program

Output:
The main() routine creates a stack object, pushes two items on it, displays the stack, pushes two
more items, and displays the stack again. Finally, it pops two items and displays the stack a third
time.
Stack (top-->bottom): 40 20
Stack (top-->bottom): 80 60 40 20 Stack (top-->bottom): 40 20

The sortedList.java Program
The sortedList.java example shown in Listing 5.6
presents a SortedList class with insert(),
remove(), and displayList() methods. Only the
insert() routine is different from its counterpart
in non-sorted lists.

Output:
In main() we insert two items with key values 20 and 40. Then we insert three more
items, with values 10, 30, and 50. These values are inserted at the beginning of the
list, in the middle, and at the end, showing that the insert() routine correctly
handles these special cases. Finally, we remove one item, to show removal is always
from the front of the list. After each change, the list is displayed.
Here’s the output from sortedList.java:
List (first-->last): 20 40
List (first-->last): 10 20 30 40 50
List (first-->last): 20 30 40 50

LISTING 5.7 The listInsertionSort.java
Program

Program

Program
This program displays the values in the array
before the sorting operation and again
afterward.
Here’s some sample output:
Unsorted array: 59 69 41 56 84 15 86 81 37 35
Sorted array: 15 35 37 41 56 59 69 81 84 86

The doublyLinked.java Program

In main() we insert some items at the beginning of the list
and at the end, display
the items going both forward and backward, delete the
first and last items and the
item with key 11, display the list again (forward only),
insert two items using the
insertAfter() method, and display the list again.
List (first-->last): 66 44 22 11 33 55
List (last-->first): 55 33 11 22 44 66
List (first-->last): 44 22 33
List (first-->last): 44 22 77 33 88

Iterator Methods
Additional methods can make the iterator a flexible and powerful class. All operations previously performed by
the class that involve iterating through the list, such as insertAfter(), are more naturally performed by the iterator.
In our example the iterator includes the following methods:
• reset()—Sets the iterator to the start of the list
• nextLink()—Moves the iterator to the next link
• getCurrent()—Returns the link at the iterator
• atEnd()—Returns true if the iterator is at the end of the list
234 CHAPTER 5 Linked Lists
• insertAfter()—Inserts a new link after the iterator
• insertBefore()—Inserts a new link before the iterator
• deleteCurrent()—Deletes the link at the iterator

LISTING 5.9 The interIterator.java
Program

Program

Output:
The main() routine inserts four items into the list, using an iterator and its insertAfter() method.
Then it waits for the user to interact with it. In the following sample interaction, the user
displays the list, resets the iterator to the beginning, goes forward two links, gets the current
link’s key value (which is 60), inserts 100 before this, inserts 7 after the 100, and displays the list
again:

Summary
A linked list consists of one linkedList object and a number of Link objects.
• The linkedList object contains a reference, often called first, to the first link
in the list.
• Each Link object contains data and a reference, often called next, to the next
link in the list.
• A next value of null signals the end of the list.
• Inserting an item at the beginning of a linked list involves changing the new
link’s next field to point to the old first link and changing first to point to the
new item.

Summary
Stacks and queues are ADTs. They can be implemented using either arrays or linked lists.
• In a sorted linked list, the links are arranged in order of ascending (or sometimes descending) key
value.
• Insertion in a sorted list takes O(N) time because the correct insertion point must be found.
Deletion of the smallest link takes O(1) time.
• In a doubly linked list, each link contains a reference to the previous link as well as the next link.
• A doubly linked list permits backward traversal and deletion from the end of the list.
• An iterator is a reference, encapsulated in a class object, that points to a link in an associated list.
• Iterator methods allow the user to move the iterator along the list and access the link currently
pointed to.
• An iterator can be used to traverse through a list, performing some operation
on selected links (or all links).

Lesson 5 link list

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