A-Level Computer Science: Data Structures Revision

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What data type is the value 7.0?

Data Structures is a core part of A-Level Computer Science. Revise the key concepts and common mistakes below, then lock them in with the free games.

Key concepts

Binary TreeEach node has up to two children.

BSTBinary search tree — left subtree smaller, right subtree larger.

ArrayA static, fixed-size collection of elements of one data type, each accessed directly by its index; it can have one or more dimensions.

RecordA collection of related, named fields that can be of different data types, such as a student's name, age and grade.

StackA last-in, first-out (LIFO) structure: push adds an item to the top, pop removes the top item, peek reads it.

QueueA first-in, first-out (FIFO) structure: items join at the rear and leave from the front; a circular queue reuses freed space.

Linked listA dynamic structure of nodes, each holding data and a pointer to the next node, so items can be inserted without shifting others.

Hash tableStores key–value pairs at an index calculated by a hash function, giving fast average lookup; collisions are handled by chaining or probing.

GraphA set of vertices joined by edges, which may be directed or weighted; stored as an adjacency matrix or an adjacency list.

Tree traversalVisiting every node in a set order: pre-order, in-order or post-order; in-order traversal of a BST outputs values in ascending order.

What your exam board covers

Where Data Structures sits in each exam board's specification. Tap a board to see what it lists.

AQAFundamentals of data structuresSpec 7517

Arrays, records, fields, tuples
Queues and stacks
Linked lists
Graphs and trees
Hash tables and dictionaries
Vectors

Source: AQA A-level Computer Science (7517) specification — Subject content, accessed 23 June 2026.

Learn Data Structures step by step

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Common mistakes to avoid

Questions where students often pick the tempting wrong answer — make sure you know the right one:

What data type is the value 7.0?✗ Integer - 7.0 is a whole number so it must be an integer. ✓ Real (float) - the decimal point makes it a real number in most languages, even though its fractional part happens to be zero.

Which item does a stack remove first?✗ The first item that was added, because items leave in arrival order. ✓ The most recently added item - stacks are LIFO, with both push and pop operating at the top.

A record differs from an array because a record:✗ Must contain elements all of the same type ✓ Can group fields of different data types under one identifier

What does in-order traversal of a binary search tree produce?✗ Nodes in the order they were inserted. ✓ Nodes in ascending sorted order.

Practise Data Structures — free games

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▶ Two Truths, One Lie ▶ Reveal Race ▶ Connections Grid ▶ Falling Words ▶ Word Web

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Data Structures

Key concepts

What your exam board covers

Common mistakes to avoid

Practise Data Structures — free games

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