A linked list is a linear data structure where each element is a separate object. Each element (we will call it a node) of a list is comprising of two items - the data and a reference to the next node. The last node has a reference to null. The entry point into a linked list is called the head of the list.

1. LINKED LISTS
LINKED LISTS 1

2. SINGLY LINKED LISTS
A singly linked list is a
concrete data
structure consisting of
a sequence of nodes
Each node stores
 element
 link to the next node
next
elem node
∅
A B C D
LINKED LISTS 2

3. INSERTING AT THE HEAD
• Allocate a new
node
• Insert new
element
• Make new node
point to old head
• Update head to
point to new
node
LINKED LISTS 3

4. REMOVING AT THE HEAD
• Update head to
point to next
node in the list
• Allow garbage
collector to
reclaim the
former first node
LINKED LISTS 4

5. INSERTING AT THE TAIL
LINKED LISTS 5
• Allocate a new
node
• Insert new element
• Have new node
point to null
• Have old last node
point to new node
• Update tail to point
to new node

6. REMOVING AT THE TAIL
• Removing at the
tail of a singly
linked list cannot
be efficient!
• There is no
constant-time
way to update the
tail to point to
the previous
node
LINKED LISTS 6

7. DOUBLY LINKED LIST
A doubly linked list is often
more convenient!
Nodes store:
 element
 link to the previous node
 link to the next node
Special trailer and header
nodes
LINKED LISTS 7
prev next
elem
trailerheader nodes/positions
elements
node

8. INSERTION
LINKED LISTS 8
A B X C
A B C
p
A B C
p
X
q
p q

9. DELETION
LINKED LISTS 9
A B C D
p
A B C
D
p
A B C

10. DELETION
LINKED LISTS 9
A B C D
p
A B C
D
p
A B C