Example We would like to keep a list of inventory records but - - PDF document

1 Linked Lists

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?

Linked List

• 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

Object next Ø Object next Object next

Linked List

• head keeps track of the head of the list
• tail keeps track of the last node in the list

– tail not always used

Object next Ø Object next Object next head tail

Insertion at Head

Object1 next Ø head Object2 next Object3 next Insert here new_node tail

Insertion at Head

• Create new_node

– store object in new_node

• Point new_node next to the node head points to

Object1 next Ø head Object2 next Object3 next new_node tail

2

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

Object1 next Ø head Object2 next Object3 next new_node tail

Insertion at Head

• Does this algorithm work for the list below?

Object1 next Ø head Object2 next Object3 next Ø head Object3 next new_node tail tail

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

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

Ø head Object3 next new_node tail

Insertion at Tail

Ø head Object3 next new_node tail Object1 next Ø head Object2 next Object3 next Insert here tail new_node

Find

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

cases

5 next Ø 3 next 12 next head tail

3

Deletion

• Deletion of head

– Complexity?

• Deletion of tail

– Complexity?

Object1 next Ø head Object2 next Object3 next tail

Insertion/Deletion in Middle

• Insert between Object1 and Object2
• Delete Object1

Object1 next Ø head Object2 next Object3 next tail

Doubly Linked Lists

• 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

Object3 prev next trailer Object2 prev next Object1 prev next header

Doubly Linked Lists

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

Object3 prev next trailer Object2 prev next Object1 prev next header trailer header

Doubly Linked Lists

• Insertion

Object3 prev next trailer Object2 prev next Object1 prev next header Object4 prev next insert here new_node

Doubly Linked Lists

• Insertion at head

1. Set next of new_node to point to what header’s next points to 2. Set prev of node that header’s next points to to point to new_node 3. Set prev of new_node to point to header 4. Set header’s next to point to new_node

• Number 1 must come before number 4
• Insertion at trailer?
• Deletion?

Object3 prev next trailer Object2 prev next Object1 prev next header Object4 prev next insert here new_node