What should I revise for my Computer Science interview?

Studying Computer Science at undergraduate level and beyond requires a very strong ability in Mathematics. 95% of students offered places at Oxford from 2021-2024 took Further Mathematics A Level (achieving at least a grade A), and Cambridge requires an A*/A in Further Mathematics A Level if it's offered by the applicant's school. Therefore, it isn't surprising that Computer Science interviews at Oxford and Cambridge consist almost entirely of mathematical problems. Applicants' technical computer science knowledge is not tested very heavily, because their experience of studying the subject varies widely: Computer Science is not required as an A Level subject by either university.

Furthermore, mathematics problems provide an excellent setting in which to assess applicants' thinking skills and approach to solving challenging problems. Interviewers aren't particularly interested in the amount of A Level/IB content (and beyond) you have memorised, though it's still important to have a good grasp on the material you have studied so far! Rather, they need to assess your ability to apply your knowledge to unfamiliar problems in creative ways. Interviewers also want to see how you can work through a problem, responding to hints and suggestions they give.

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What type of questions should I prepare for?

The topics that arise in Computer Science interviews are similar to those in Mathematics interviews, so you might expect to encounter:

• Graph sketching

• Combinatorics (counting permutations and choices)

Integration is often emphasised a little less than in Mathematics interviews. Computer Science interviews tend to place more emphasis on:

• Recursion

• Probability

• Number theory

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In the past few years, we have also observed that questions involving pseudocode have become more common. In these questions, students are presented with some code in an informal programming language. They need to identify what it does, and how it could be modified to achieve certain tasks. In other cases, an applicant might be asked to sketch out an algorithm for achieving a certain task. Suitable practice questions can be quite difficult to come by, but such problems are included as part of our Interview Preparation Programme.

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Key Results and Formulae to Memorise

Solving interview problems requires nuance: the ability to recite knowledge is not what interviewers are looking for in prospective students. That being said, there are certain key results and formulae that are helpful to memorise in case they can be applied to the problems you are presented with.

• Arithmetic and geometric series formulae
  They are often needed as the final blow in solving a problem and demonstrating clear fluency will help to impress your interviewers.

• Counting principles
  Basic counting of permutations and choices may be useful; for example, the formula for 'n choose r' in terms of factorials, and basic principles for counting permutations.

• Standard graphs such as logarithms, exponentials, trigonometric functions, and polynomials
  You should be able to work these out effortlessly. You are unlikely to spend much time sketching one of these specific graphs, but they will form the basic building blocks of more challenging graphs which you're likely to be confronted with.

• Standard trig values
  You should be able to recall these instantly. It will not impress your interviewer if you have to draw a triangle in order to calculate them!

• Fundamentals of probability
  This includes the conditional probability formula, basic proportionality distributions (e.g. binomial distribution) and the definition of expectation.

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Will I be asked about my personal statement?

People often liken university interviews to job interviews, which usually focus on an applicant's motivation to apply for the job and their soft skills/personal qualities, such as teamwork or time management. Whilst some universities might take this approach, interviews at Oxford and Cambridge typically focus almost entirely on academic ability and potential. Interviewers need to find out whether an applicant is well-suited to the style of small group teaching at Oxford and Cambridge (tutorials at the former, supervisions at the latter) and able to thrive in an intense academic environment. Having said this, confident communication and showing enthusiasm for your subject is still important!

For mathematical subjects such as Computer Science, it is unlikely that you will be asked about your personal statement or motivation to apply for the course at any great length. Such questions usually serve as ice-breakers and likely have little bearing on the outcome of the interview. However, you should still be prepared to discuss anything you mentioned in your personal statement, just in case. It's wise to prepare an answer to the predictable 'why have you applied to this university/course/college?' and practise conveying your passion for the subject.

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Further Advice

Though it is important to ensure that you have a good grasp of the topics and concepts mentioned in this article, it is crucial to practise applying these concepts to interview-style problems. Authentic interview questions can be difficult to find, but practising any challenging maths problems - and explaining your reasoning aloud - is useful preparation. To see our recommended free resources, visit 'Oxbridge Interview Preparation Resources' on our Knowledge Base.

You can also visit our YouTube channel to see two real Computer Science interview questions, complete with fully worked solutions:

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If you're looking for more practice materials and specialist guidance, consider joining our Interview Preparation Programme. At Vantage Admissions, we support prospective Computer Science students with all aspects of their application, from the MAT and TMUA to interview preparation. Our Interview Preparation Programme includes a comprehensive, pre-recorded course of six lessons, designed to cover the common topics that arise in interview questions (including those listed above!). We also offer a question bank of 80 real Computer Science interview questions, complete with detailed solutions, and authentic mock interviews with real Oxbridge interviewers. Visit our Interview page to find out more.