cs350: data structures linked lists - ycpcs.github.io file- singly linked lists - doubly linked...
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CS350: Data Structures © James Moscola
College Catalog2009–2011
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College Catalog2009–2011
!"#$%&'())*+,-.)/.&01234546708.9:;*&<:(#.="#>&1015?26511??@A9/**/")*&<B!&C(>&1015?2D50633
05?3352775?30?EEEF+C:F(A;
!""#$%%&'$#()*$&+$,-$%.$"
'GHI<GJHK&L<MNK'GONJHK&P@JJHGMFIF&'<IJ@QH&'@OK
!<GR%&'@'HGPOJ&N<F&012
YO
RK
CO
LLEGE O
F PENN
SY
LVA
NIA
CO
LLEGE C
ATA
LOG
2009–2011
!""#$%&'()*+,--.../ 012$1$"..."34#3$4.56
College Catalog2009–2011
!"#$%&'())*+,-.)/.&01234546708.9:;*&<:(#.="#>&1015?26511??@A9/**/")*&<B!&C(>&1015?2D50633
05?3352775?30?EEEF+C:F(A;
!""#$%%&'$#()*$&+$,-$%.$"
'GHI<GJHK&L<MNK'GONJHK&P@JJHGMFIF&'<IJ@QH&'@OK
!<GR%&'@'HGPOJ&N<F&012
YO
RK
CO
LLEGE O
F PENN
SY
LVA
NIA
CO
LLEGE C
ATALO
G 2009–2011
!""#$%&'()*+,--.../ 012$1$"..."34#3$4.56
James MoscolaDepartment of Engineering & Computer ScienceYork College of Pennsylvania
CS350: Data StructuresLinked Lists
CS350: Data Structures
Linked Lists
• Come in a variety of different forms - singly linked lists- doubly linked lists- circular linked lists
• Composed of a set of nodes that hold data and contain one or more pointers to neighboring nodes in the list - singly linked lists contain only a pointer to the next node in the list- doubly linked lists contain a pointer to the next node and the
previous node in the list
2
data
CS350: Data Structures
Linked List Operations
• Basic operations include: - insert / add- remove
• Additional operations may include: - getFirst- getLast- find- isEmpty- makeEmpty
3
CS350: Data Structures
Linked List Insertion
• Basic implementation uses a head pointer that points to the first node in the list - Points to NULL upon initialization when no nodes exist in the list
• Depending on implementation, insertion may take place at the head of the list, at the tail of the list, or at some other specified node
4
head
NULL
CS350: Data Structures
Linked List Insertion
5
Start with Empty List
head points to the front of the linked list
tail points to the back of the linked list
head
NULL
tail
CS350: Data Structures
null
Linked List Insertion
6
head
Insert Value: A
NULLA
tail
CS350: Data Structures
null
Linked List Insertion
7
head
Insert Value: B
nullA
tail
NULLB
CS350: Data Structures
null
Linked List Insertion
8
head
Insert Value: C
nullA
tail
nullB NULLC
CS350: Data Structures
null
Linked List Removal
9
head
Remove First Value:
nullA
tail
nullB NULLC
CS350: Data Structures
Linked List Removal
• Removing last value is not very efficient when using singly linked lists - Want to make next-to-last node in list the last node- Must traverse entire list, starting from the head, to find the next-to-
last node in the list- O(N)
10
null
head
nullA
tail
nullB NULLC
CS350: Data Structures
Linked List Implementation
11
public class LinkedListNode<E> {public E data;public LinkedListNode<E> next;
}
CS350: Data Structures
Linked List Implementation
12
// Inserts at the tail of the list
public void insert (E data) {LinkedListNode<E> newNode = new LinkedListNode<E>();newNode.data = data; // assign data to newNodetail.next = newNode;tail = newNode;
}
This method is oversimplified, what happens if this is called when the list is empty?
CS350: Data Structures
Linked List Implementation
13
// Inserts at the tail of the list
public void insert (E data) {LinkedListNode<E> newNode = new LinkedListNode<E>();newNode.data = data; // assign data to newNodeif (isEmpty()) {
head = tail = newNode;} else {
tail.next = newNode;tail = newNode;
}}
Fixed insert method
CS350: Data Structures
Linked List Implementation
14
// Inserts at the head of the list
public void insertAtHead (E data) {LinkedListNode<E> newNode = new LinkedListNode<E>();newNode.data = data; // assign data to newNodenewNode.next = head;head = newNode;
}
This method is oversimplified, what happens if this is called when the list is empty?
CS350: Data Structures
Linked List Implementation
15
// Inserts at the head of the list
public void insertAtHead (E data) {LinkedListNode<E> newNode = new LinkedListNode<E>();newNode.data = data; // assign data to newNodenewNode.next = head;
if (!isEmpty()) {head = newNode;
} else {head = tail = newNode;
}}
CS350: Data Structures
Linked List Implementation
16
// Removes node from head of list and returns its value
public E remove() {if (head != null) {
E nodeData = head.data;head = head.next;return nodeData;
} else {return null;
}}
CS350: Data Structures
Considerations for Linked List Implementation
• Implementation as previously shown requires a error checking in the insert and remove methods to check for edge cases (i.e. checking for an empty list)
• To improve the speed of the Linked List operations, it is possible to remove these tests - Tradeoff: speedup comes at the expense of one additional ‘dummy’
node in the Linked List
• Idea: create a dummy node that exists in the linked list at ALL times ... it is created as part of the list and points to the head node
- Eliminates the need to always check for NULL
- Generalized the insert and remove methods
17
CS350: Data Structures
• Implementation as previously shown requires error checking in the insert and remove methods to check for edge cases (i.e. checking for an empty list)
null NULL null
Linked List with Header Node
18
head
NULLA
tail
NULL NULL
head
tail
Empty list List with single node
CS350: Data Structures
Linked List Implementation
19
// Inserts at the tail of the list // When using dummy header node, no need to test for null
public void insert (E data) {LinkedListNode<E> newNode = new LinkedListNode<E>();newNode.data = data; // assign data to newNodetail.next = newNode;tail = newNode;
}
CS350: Data Structures
Linked List Implementation
20
// Inserts at the head of the list
public void insertAtHead (E data) {LinkedListNode<E> newNode = new LinkedListNode<E>();newNode.data = data; // assign data to newNodenewNode.next = head.next;head.next = newNode;
}
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