Essential algorithms and data structures for GCSE & A’Level

The aim of this book is to provide students and teachers of GCSE, AS & A level Computer Science a comprehensive guide to the algorithms students need to understand for examinations.  Each chapter examines a data structure or algorithm explaining how it works, real-world applications, a step-by-step example, pseudocode, actual code in two languages and a description of the space and time complexity.

We have chosen to provide coded solutions in Python 3 because it is the most popular language taught at GCSE, and in Visual Basic Console (2015 onwards) because it is a language that most closely resembles the pseudocode and coded examples students will need to work with in examinations.

These coded solutions can be downloaded from

This book is appropriate for all English and Welsh Computer Science specifications, check out our up-to-date mapping document for details.

Select the appropriate tile below for additional videos and resources relating to each algorithm.

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Make sure to download our double-sided Big O notation cheat sheet to help you get to grips with algorithm complexity.  (Select the image below to download).