Linked Lists (Cambridge International A-Level Computer Science)

Exam board Cambridge International · A-LevelUpdated 2025-06-03

Linked lists

How do you program a linked list?

To recap the main operations of linked lists and how they work, read our ADT Overview page
To program a Linked List you must be able to perform the following operations:
- Create a linked list
- Traverse a linked list
- Add data to a linked list
- Remove data from a linked list

Create a linked list

Define the class called ‘Node’ that represents a node in the linked list.
Each node has 2 fields ‘fruit’ (this stores the fruit value) and ‘next’ (this stores a reference to the next node in the list)
We create 3 nodes and assign fruit values to each node
To establish a connection between the nodes we set the ‘next’ field of each node to the appropriate next node

Pseudocode

Python

Java

Algorithm to traverse a linked list

We traverse the linked list starting from ‘node1’. We output the fruit value of each node and update the ‘current’ reference to the next node until we reach the end of the list

Pseudocode

Python
`# Traverse the linked list` `current = node1` `while current is not None:` `print(current.fruit)` `current = current.next`

Java
`// Traverse the linked list` `current = node1;` `while (current != null) {` `System.out.println(current.fruit);` `current = current.next;`

Algorithm to add data to a linked list

We create a new node with the new data and check if the list is empty
If it isn’t, we find the last node and add the new node to the end

Pseudocode

Python
`# Add "orange" to the end of the linked list` `new_node = Node("orange")` `if node1 is None:` `# If the list was empty, make "orange" the head` `node1 = new_node` `else:` `# Find the last node and append "orange" to it` `current = node1` `while current.next is not None:` `current = current.next` `current.next = new_node`

Java
`// Add "orange" to the end of the linked list` `Node new_node = new Node("orange");` `if (node1 == null) {` `// If the list was empty, make "orange" the head` `node1 = new_node;` `} else {` `// Find the last node and append "orange" to it` `current = node1;` `while (current.next != null) {` `current = current.next;` `}` `current.next = new_node;` `}`

Algorithm to remove data from a linked list

We traverse the list until we find the data to be removed
If the data to be removed is the first node, we update the head, else we update the node before to bypass the data to be removed

Pseudocode

Python
`# Find and remove "apple"` `while current is not None:` `if current.fruit == "apple":` `if previous is None:` `# If "apple" is the first node, update the head` `node1 = current.next` `else:` `# Remove the node by updating the previous node's next pointer` `previous.next = current.next` `break` `previous = current` `current = current.next`

Java
`// Find and remove "apple"` `while (current != null) {` `if (current.fruit.equals("apple")) {` `if (previous == null) {` `// If "apple" is the first node, update the head` `node1 = current.next;` `} else {` `// Remove the node by updating the previous node's next pointer` `previous.next = current.next;` `}` `break;` `}` `previous = current;` `current = current.next;` `}`

Worked Example The following diagram represents an Abstract Data Type (ADT) for a linked list.

The free list is as follows:

Explain how a node containing data value B is added to the list in alphabetic sequence.[4]

Final answer: Answer

One mark per point

Check for a free node [1 mark]

Search for correct insertion point [1 mark]

Assign data value B to first node in free list / node pointed to by start pointer of free list [1 mark]

Pointer from A will be changed to point to node containing B (instead of C) [1 mark]

Pointer from B will be changed to point to node containing C [1 mark]

Start pointer in free list moved to point to next free node [1 mark]

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Exam Questions Flashcards

Pseudocode

Python

Java

Pseudocode

Python

# Traverse the linked list

current = node1

while current is not None:

print(current.fruit)

current = current.next

Java

// Traverse the linked list

current = node1;

while (current != null) {

System.out.println(current.fruit);

current = current.next;

Pseudocode

Python

# Add "orange" to the end of the linked list
new_node = Node("orange")

if node1 is None:
# If the list was empty, make "orange" the head
node1 = new_node
else:
# Find the last node and append "orange" to it
current = node1
while current.next is not None:
current = current.next
current.next = new_node

Java

// Add "orange" to the end of the linked list
Node new_node = new Node("orange");

if (node1 == null) {
// If the list was empty, make "orange" the head
node1 = new_node;
} else {
// Find the last node and append "orange" to it
current = node1;
while (current.next != null) {
current = current.next;
}
current.next = new_node;

}

Pseudocode

Python

# Find and remove "apple"

while current is not None:

if current.fruit == "apple":

if previous is None:

# If "apple" is the first node, update the head

node1 = current.next

else:

# Remove the node by updating the previous node's next pointer

previous.next = current.next

break

previous = current

current = current.next

Java

// Find and remove "apple"

while (current != null) {

if (current.fruit.equals("apple")) {

if (previous == null) {

// If "apple" is the first node, update the head

node1 = current.next;

} else {

// Remove the node by updating the previous node's next pointer

previous.next = current.next;

}

break;

}

previous = current;

current = current.next;

}