Singly

Linked Lists

Objectives

• Define what a Singly Linked List is
• Compare and contrast Linked Lists with Arrays
• Implement insertion, removal and traversal methods on Singly Linked Lists

What is a linked list?

Singly Linked Lists

null

next

next

next

4

6

8

2

HEAD

TAIL

LENGTH = 4

Comparisons with Arrays

Lists 

• Do not have indexes!
• Connected via nodes with a next pointer
• Random access is not allowed

Arrays

• Indexed in order!
• Insertion and deletion can be expensive
• Can quickly be accessed at a specific index

Pushing

Adding a new node to the end of the Linked List!

Pushing pseudocode

Let's visualize this!

• This function should accept a value
• Create a new node using the value passed to the function
• If there is no head property on the list, set the head and tail to be the newly created node
• Otherwise set the next property on the tail to be the new node and set the tail property on the list to be the newly created node
• Increment the length by one
• Return the linked list

YOUR

TURN

Popping

Removing a node from the end of the Linked List!

Popping pseudocode

Let's visualize this!

• If there are no nodes in the list, return undefined
• Loop through the list until you reach the tail
• Set the next property of the 2nd to last node to be null
• Set the tail to be the 2nd to last node
• Decrement the length of the list by 1
• Return the value of the node removed

YOUR

TURN

Shifting

Removing a new node from the beginning of the Linked List!

Shifting pseudocode

Let's visualize this!

• If there are no nodes, return undefined
• Store the current head property in a variable
• Set the head property to be the current head's next property
• Decrement the length by 1
• Return the value of the node removed

YOUR

TURN

Unshifting

Adding a new node to the beginning of the Linked List!

Unshifting pseudocode

Let's visualize this!

• This function should accept a value
• Create a new node using the value passed to the function
• If there is no head property on the list, set the head and tail to be the newly created node
• Otherwise set the newly created node's next property to be the current head property on the list
• Set the head property on the list to be that newly created node
• Increment the length of the list by 1
• Return the linked list

YOUR

TURN

Get

Retrieving a node by it's position in the Linked List!

Get pseudocode

Let's visualize this!

• This function should accept an index
• If the index is less than zero or greater than or equal to the length of the list, return null
• Loop through the list until you reach the index and return the node at that specific index

YOUR

TURN

Set

Changing the value of a node based on it's position in the Linked List

Set pseudocode

Let's visualize this!

• This function should accept a value and an index
• Use your get function to find the specific node.
• If the node is not found, return false
• If the node is found, set the value of that node to be the value passed to the function and return true

YOUR

TURN

Insert

Adding a node to the Linked List at a specific position

Insert pseudocode

• If the index is less than zero or greater than the length, return false
• If the index is the same as the length, push a new node to the end of the list
• If the index is 0, unshift a new node to the start of the list
• Otherwise, using the get method, access the node at the index - 1
• Set the next property on that node to be the new node
• Set the next property on the new node to be the previous next
• Increment the length
• Return true

YOUR

TURN

Remove

Removing a node from the Linked List at a specific position

Remove pseudocode

Let's visualize this!

• If the index is less than zero or greater than the length, return undefined
• If the index is the same as the length-1, pop
• If the index is 0, shift
• Otherwise, using the get method, access the node at the index - 1
• Set the next property on that node to be the next of the next node
• Decrement the length
• Return the value of the node removed

YOUR

TURN

REVERSE

Reversing the Linked List

in place!

13

27

32

71

HEAD

TAIL

REVERSING A SINGLY LINKED LIST

Reverse pseudocode

Let's visualize this!

• Swap the head and tail
• Create a variable called next
• Create a variable called prev
• Create a variable called node and initialize it to the head property
• Loop through the list
• Set next to be the next property on whatever node is
• Set the next property on the node to be whatever prev is
• Set prev to be the value of the node variable
• Set the node variable to be the value of the next variable
• Once you have finished looping, return the list

YOUR

TURN

Big O

of Singly Linked Lists

RECAP

• Singly Linked Lists are an excellent alternative to arrays when insertion and deletion at the beginning are frequently required
• Arrays contain a built in index whereas Linked Lists do not
• The idea of a list data structure that consists of nodes is the foundation for other data structures like Stacks and Queues