Linked Lists

1
Linked Lists
2
Example

• We would like to keep a list of inventory records
  but only as many as we need
• An array is a fixed size
• Instead use a linked list
• What are the disadvantages of using a linked list?

3
Linked List
Object
Object
Object
next
next
next
Ø

• Node one element of the linked list
• Object data stored in the node examples?
• next a reference to the next node in the list
• last node points to NULL

4
Linked List
tail
Object
Object
Object
head
next
next
next
Ø

• head keeps track of the head of the list
• tail keeps track of the last node in the list
• tail not always used

5
Insertion at Head
tail
new_node
Object1
Object2
head
next
next
Ø
Object3
Insert here
next
6
Insertion at Head
tail
new_node
Object1
Object2
head
next
next
Ø
Object3
next

• Create new_node
• store object in new_node
• Point new_node next to the node head points to

7
Insertion at Head
tail
new_node
Object1
Object2
head
next
next
Ø
Object3
next

• Create new_node
• store object in new_node
• Point new_node next to the node head points to
• Point head to new_node

8
Insertion at Head
tail
Object1
Object2
Object3
head
next
next
next
Ø

• Does this algorithm work for the list below?

new_node
tail
Ø
head
Object3
next
9
Insertion at Head

• Create new_node
• store object in new_node
• Point new_node next to the node head points to
• Point head to new_node
• If tail points to NULL
• point tail to new_node

10
Insertion at Head
new_node
tail
Ø
head
Object3
next

• Create new_node
• store object in new_node
• Point new_node next to the node head points to
• Point head to new_node
• If tail points to NULL
• point tail to new_node

11
Insertion at Tail
tail
Object1
Object2
head
next
next
Ø
Object3
Insert here
new_node
next
new_node
tail
Ø
head
Object3
next
12
Find
tail
5
3
12
head
next
next
next
Ø

• find(3)
• find(16) - always remember to deal with special
  cases

13
Deletion
tail
Object1
Object2
Object3
head
next
next
next
Ø

• Deletion of head
• Complexity?
• Deletion of tail
• Complexity?

14
Insertion/Deletion in Middle
tail
Object1
Object2
Object3
head
next
next
next
Ø

• Insert between Object1 and Object2
• Delete Object1

15
Exercises

• Implement a method to recursively count number of
  nodes in a linked list
• Implement a method to reverse a linked list
• Implement a method that takes as input two
  integers representing node positions and swaps
  the specified nodes

16
Doubly Linked Lists
Object3
Object2
Object1
header
prev
prev
prev
trailer
next
next
next

• Each node keeps a pointer to the next node and to
  the previous node
• Makes some operations (such as insertion at end)
  more efficient
• Costs?
• At the beginning and end of the list are sentinel
  nodes
• Simplify insertion/deletion algorithm

17
Doubly Linked Lists
Object3
Object2
Object1
header
prev
prev
prev
trailer
next
next
next

• Insertion and deletion at beginning/end
• Insertion and deletion in middle

trailer
header
18
Doubly Linked Lists
new_node
Object4
prev
insert here
next
Object3
Object2
Object1
header
prev
prev
prev
trailer
next
next
next

• Insertion

19
Doubly Linked Lists
new_node
Object4
prev
insert here
next
Object3
Object2
Object1
header
prev
prev
prev
trailer
next
next
next

• Insertion at head
• Set next of new_node to point to what headers
  next points to
• Set prev of node that headers next points to to
  point to new_node
• Set prev of new_node to point to header
• Set headers next to point to new_node
• Number 1 must come before number 4
• Insertion at trailer?
• Deletion?