Cambridge Computer Science interview

The Cambridge Computer Science interview is mostly problem-solving. After a brief chat about your interest in the subject, you talk through multi-step algorithm, logic and maths problems out loud, and the interviewers give hints when you're stuck or heading the wrong way. Most applicants have two interviews of 20 to 30 minutes, often one leaning computer science and one leaning maths, in December 2026 (main period 7 to 18 December), online or in person depending on the College. No programming is assumed.

Key facts

What happens in the interview

Computer Science interviews are mostly problem-solving, and the problems almost always need maths. Some are pure maths, while others focus more on algorithms or other ideas in computer science, such as programming and logic. They are loosely based on computer science but don't test specific knowledge or a programming language, and you won't be asked about anything outside your school curriculum.

A computer science interview usually opens with a brief chat about your interest in the subject or a project you mention: what you built, which algorithm you chose and why. Then it moves on to multi-step problems.

Interviewers run it as a conversation:

• They let you take time to think before you start.
• They ask you to explain your approach.
• They give a hint if you're stuck or heading the wrong way.
• They ask you to try small cases, and whether a method always works and how efficient it is.
• If you solve something quickly, they move on.

Not completing every problem is expected. Getting stuck and finding a way through with help is exactly what interviewers want to see.

You'll work on paper, or on a tablet online, and may be asked to share your working. Have paper and a pen beside you, or a tablet if your College asks for one (Trinity requires one online).

What interviewers look for

Cambridge's Computer Science interviewers look for:

• Logical reasoning and problem-solving: breaking a multi-step problem down and justifying each step.
• Mathematical ability: the department's main focus, because maths underpins much of the course.
• Your approach to an unfamiliar problem: how you tackle something new and use guidance.
• Motivation for the subject: being able to explain what you've built or explored, and why you made the choices you did.

Toby's practice interview scores five criteria: mathematical knowledge, logical reasoning and problem-solving, algorithmic thinking (seeing the procedure or structure behind a problem, trying small cases, and thinking about efficiency and correctness), explaining your approach, and motivation for computer science.

How the interview is marked

Cambridge doesn't publish a marking scale for Computer Science interviews. The department says the TMUA won't make or break an application and every part is considered together: Colleges weigh the interview with your grades, the TMUA (and the CSAT at Peterhouse and Trinity) and the rest of your application. The CSAT's provider says there are no pass marks for either the interview or the CSAT.

Anyone can have an interview that doesn't go to plan, and a bad interview isn't the end of an application.

Example questions

These are problems published by Oxford and by a Cambridge College, in the form Toby asks them: two from computer science and one from maths. Interviewers set their own questions, so yours will differ.

Searching for the maximum

Published by Oxford Computer Science: sample interview problems

The real-valued function f(x), defined for 0 ≤ x ≤ 1, has a single maximum at x = m. If 0 ≤ u < v ≤ m then f(u) < f(v), and if m ≤ u < v ≤ 1 then f(u) > f(v). You are told nothing else about f, but you may ask for the value of f(x) for any values of x you choose. How would you find the approximate value of m?

• Why interviewers ask it: it shows whether you can design a search that narrows down an answer, and count its cost carefully enough to improve it.
• A hint an interviewer might give: "Suppose I tell you f of a half is 7. What does that tell you about where m is?"
• A strong answer works out how much each question about f really tells you, uses the shape of the graph to decide which part of the interval to throw away, then counts how many evaluations each round costs and looks for a way to waste fewer.
• A common slip is thinking a single value shows which side of the peak you're on.

Death by chocolate

Published by Oxford Computer Science: sample interview problems

You are locked in a room with your worst enemy. On a table in the centre of the room is a bar of chocolate, divided into squares in the usual way. One square of the chocolate is painted with a bright green paint that contains a deadly poison. You and your enemy take it in turns to break off one or more squares from the remaining chocolate (along a straight line) and eat them. Whoever is left with the green square must eat it and die in agony. You may look at the bar of chocolate and then decide whether to go first or second. Describe your strategy.

• Why interviewers ask it: it shows whether you simplify a game to small cases, find which positions are winning and losing, and spot when a game splits into independent parts.
• A hint an interviewer might give: "Suppose the bar is a single row with the poison at one end. What should you do?"
• A strong answer starts with a single row of chocolate, finds a strategy there and explains why it works, then builds up to bigger bars and describes a position by a few simple numbers.
• A common slip is trying to analyse a large bar head-on instead of starting with a single row.

The nth derivative of 1/x

Published by Lucy Cavendish College, Cambridge: Interview Question Pack (Sciences & Maths)

Come up with a rule for the nth derivative of 1/x: a formula that works for every n.

• Why interviewers ask it: it shows whether you can spot a pattern from a few cases, state it precisely and prove it by induction.
• A hint an interviewer might give: "Write 1/x as x to the power −1. What are the first three derivatives?"
• A strong answer works out three or four derivatives carefully before guessing, states the rule exactly and checks it, then proves it by induction, showing clearly where each new factor comes from.
• A common slip is checking a few cases and calling it a proof.

Practise with Toby

Toby is an AI interviewer that runs practice interviews by voice. The Cambridge Computer Science interview is built from Cambridge's admissions pages, the Department of Computer Science and Technology and College admissions pages, and follows the common pattern of two interviews:

• Computer science interview. A brief chat about your interest in the subject or a project, then multi-step problems on algorithms, logic, games, graphs and counting, explained aloud as you go.
• Maths interview. School maths at TMUA level and beyond: functions and graphs, calculus, sequences and series, number theory, proof and probability, worked through with hints.

It draws on 44 problems, each with hints and follow-ups. Eighteen are published problems from Cambridge and Oxford sources, and the rest were written to the same style and level, with every result independently re-derived. No programming is needed: you talk each problem through.

Toby puts the problem on screen, gives you time to think and asks you to talk it through. He gives a hint only when you're stuck, asks why, and asks whether your method always works and how efficient it is. Like a real interviewer, he doesn't praise every answer.

You can add your personal statement so Toby can ask about a project you mention, and choose a 10, 20 or 30-minute interview. Your prep page has the format, what interviewers look for and practice problems with hints and worked solutions. Afterwards, your debrief gives you a practice mark out of 10 (6 is acceptable, 7 good, 8 strong), a score against each criterion, notes on every question and the full transcript. A practice mark is a guide, not a prediction.

Frequently asked questions

Sources

Last checked October 2026.

• University of Cambridge: Computer Science
• University of Cambridge: Interviews
• University of Cambridge: Preparing for interview
• University of Cambridge: Admission tests
• Cambridge Computer Science and Technology: Interviews
• Cambridge Computer Science and Technology: Admissions FAQs
• Oxford Computer Science: Sample interview problems
• Lucy Cavendish College, Cambridge: Interview Question Pack (Sciences & Maths)

Related interviews

• Oxford Computer Science interview
• Oxford Mathematics and Computer Science interview
• Cambridge Mathematics interview

All Oxford and Cambridge interviews·University admissions

Toby is independent and isn't affiliated with or endorsed by the University of Oxford or the University of Cambridge.