Linked List

1
Chapter 17

• Linked List

2
Objective

• Linked lists
• basic ideas header nodes and iterator classes
• Implementation details
• doubly linked lists
• circular linked lists

3
arrayname

• Arrays
• contiguous
• direct access of elements
• insertion / deletion difficult
• Linked Lists
• noncontiguous
• must scan for element
• insertion /deletion easy

4
Iterating through a data structure
a
for (int i 0 i lt length i) coutltlt
ai for (ListNode p theList.first p !
null p p.next) coutltlt p.data
5
Adding an element
A0
A1
A2
first
last
class ListNode Object data ListNode
next At any point, we can add a new last item
x by doing this Last-gtnext new
ListNode() Last Last-gtnext Last-gtdata
x Last-gtnext null
6
A0
A1
A2
first
last
class ListNode Object data ListNode
next At any point, we can add a new last item
x by doing this Last-gtnext new
ListNode() Last Last-gtnext Last-gtdata
x Last-gtnext null
7
A0
A1
A2
first
last
class ListNode Object data ListNode
next At any point, we can add a new last item
x by doing this Last-gtnext new
ListNode() last last-gtnext Last-gtdata
x Last-gtnext null
8
A0
A1
A2
x
first
last
class ListNode Object data ListNode
next At any point, we can add a new last item
x by doing this last-gtnext new
ListNode() last last-gtnext Last-gtdata
x Last-gtnext null
9
A0
A1
A2
x
first
last
class ListNode Object data ListNode
next At any point, we can add a new last item
x by doing this Last-gtnext new
ListNode() last last-gtnext Last-gtdata
x Last-gtnext null
10
Inserting an element
A0
A1
A2
current
first
last
class ListNode Object element ListNode
next At any point, we can add a new last item
x by doing this tmp new ListNode() Tmp-gtele
ment x Tmp-gtnext current-gtnext Current-gtnext
tmp
11
A0
A1
A2
current
first
last
class ListNode Object element ListNode
next At any point, we can add a new last item
x by doing this tmp new ListNode() Tmp-gtele
ment x Tmp-gtnext current-gtnext Current-gtnext
tmp
tmp
12
A0
A1
A2
current
x
first
last
class ListNode Object element ListNode
next At any point, we can add a new last item
x by doing this tmp new ListNode() Tmp-gtele
ment x Tmp-gtnext current-gtnext Current-gtnext
tmp
tmp
13
A0
A1
A2
current
x
first
last
class ListNode Object element ListNode
next At any point, we can add a new last item
x by doing this tmp new ListNode() Tmp-gtele
ment x Tmp-gtnext current.next current-gtnext
tmp
tmp
14
A0
A1
A2
current
x
first
last
class ListNode Object element ListNode
next At any point, we can add a new last item
x by doing this tmp new ListNode() Tmp-gtele
ment x Tmp-gtnext current-gtnext Current-gtnext
tmp
tmp
15
Simplified version

• Current-gtnext new ListNode(x, current-gtnext)

16
Deleting an element
A0
A1
A2
current
last
class ListNode Object element ListNode
next Current-gtnext current-gtnext-gtnext
17
Deleting an element
A0
A1
A2
current
last
class ListNode Object element ListNode
next Current-gtnext current-gtnext-gtnext
Memory leak!
18
Delete a Node

• Node deletedNode current-gtnext
• Current-gtnext current-gtnext-gtnext
• Delete deletedNode

19
Header Nodes
a
b
c
header
Header nodes allow us to avoid special cases in
the code such as insertion of the first element
and removal of the last element. The header node
holds no data but serves to satisfy the
requirement that every node have a previous
node. Not necessarily a standard implementation.
20
C implementation

• We have a list.
• This list consists of listNodes.
• In order to access these listNodes, we need an
  iterator.
• Code online

21
Doubly Linked Lists
a
b
c
head
tail
Consider how hard it is to back up in a singly
linked list. Also consider text editor example
class DoubleListNode Object element
ListNode next ListNode prev
22
Empty Doubly Linked List
c
head
tail
// constructor DoubleList() head new
DoubleListNode () tail new DoubleListNode
() head-gtnext tail tail-gtprev
head
23
Inserting into a Doubly Linked List
a
c
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
24
Inserting into a Doubly Linked List
a
c
b
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
25
Inserting into a Doubly Linked List
a
c
b
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
26
Inserting into a Doubly Linked List
a
c
b
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
27
Inserting into a Doubly Linked List
a
c
b
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
28
Inserting into a Doubly Linked List
a
c
b
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
29
Inserting into a Doubly Linked List
a
c
b
head
tail
current
newNode new DoublyLinkedListNode() newNode-gtprev
current newNode-gtnext current-gtnext newNode
-gtprev-gtnext newNode newNode-gtnext-gtprev
newNode current newNode
30
Deleting an element from a double linked list
a
c
b
head
current

• oldNodecurrent
• oldNode-gtprev-gtnext oldNode-gtnext
• oldNode-gtnext-gtprev oldNode-gtprev
• current oldNode-gtprev
• delete oldNode

31
Deleting an element from a double linked list
a
c
b
head
current
oldNode
oldNodecurrent oldNode-gtprev-gtnext
oldNode-gtnext oldNode-gtnext-gtprev
oldNode-gtprev current oldNode-gtprev delete
oldNode
32
Deleting an element from a double linked list
a
c
b
head
current
oldNode
oldNodecurrent oldNode-gtprev-gtnext
oldNode-gtnext oldNode-gtnext-gtprev
oldNode-gtprev current oldNode-gtprev delete
oldNode
33
Deleting an element from a double linked list
a
c
b
head
current
oldNode
oldNodecurrent oldNode-gtprev-gtnext
oldNode-gtnext oldNode-gtnext-gtprev
oldNode-gtprev current oldNode-gtprev delete
oldNode
34
Deleting an element from a double linked list
a
c
b
head
current
oldNode
oldNodecurrent oldNode-gtprev-gtnext
oldNode-gtnext oldNode-gtnext-gtprev
oldNode-gtprev current oldNode-gtprev delete
oldNode
35
Deleting an element from a double linked list
a
c
head
current
oldNodecurrent oldNode-gtprev-gtnext
oldNode-gtnext oldNode-gtnext-gtprev
oldNode-gtprev current oldNode-gtprev delete
oldNode
36
Circular Linked lists
a
b
c
d
first
37
Sorted Linked List
A sorted link list is one in which items are in
sorted order. It can be derived from a list
class. code
38
Common errors (Page 599 )

• Splicing in nodes incorrectly when performing
  insertion
• Forgetting incomplete class declaration
• Calling delete at wrong time during remove()
• More errors on page 599 are given

39
In class exercises

• Question 17.7 from the book.
• Suppose that you have a pointer to a node in
  singly linked list that guaranteed not to be the
  last node in the list. You do not have pointers
  to any other nodes (except by following links).
  Describe an O(1) algorithm that logically removes
  the value stored in such a node from the linked
  list, maintaining the integrity of the linked
  list (Hint Involve the next node)

40
In class exercises

• Question 17.3 from the book.
• Write an algorithm for printing a singly linked
  list in reverse. (Dont use recursion).