Interviews
The questions top companies actually ask
The twenty questions top companies actually ask, chosen from real interview reports rather than asserted, each one with the evidence behind it, a model answer, and the clearest explanation of the underlying idea we could find.
20 questions · 4 rounds · 18 companies named in the evidence · 2 free
The coding round
Write correct code while thinking out loud, and reach for the structure the shape of the data is asking for.
- Given a list of intervals, merge all the overlapping ones.Whether you sort before you scan, and whether you can say why sorting is what makes one pass sufficient.
- Find the lowest common ancestor of two nodes in a binary tree.Whether you can reason recursively about a tree without drawing the whole thing, and whether you notice what the tree guarantees.
- Design an algorithm to serialise and deserialise a binary tree.Whether you can design a format, not just an algorithm, and whether you make the null markers explicit.
- You are given two numbers as linked lists of digits in reverse order. Add them and return the sum as a linked list.Whether you carry correctly and whether you handle the two lists being different lengths without writing the loop twice.
- Given an elevation map, compute how much water it can trap after raining.Whether you can find the local rule, that water above a column is decided by the tallest bar on each side, before optimising.
- Given a list of directory paths and file contents, find all the groups of duplicate files.Whether you reach for a hash map keyed on content, and whether you think about what this costs on real files.
- Implement Conway's Game of Life, updating the board in place.Whether you notice that a naive in-place update corrupts the neighbours the next cell still needs.
The system design round
Bound the problem, pick a data model, and be honest about what your design gives up.
- Design a multi-threaded web crawler.Whether you make the frontier explicit, and whether politeness and deduplication appear before you are prompted.
- Design a chat server.Whether you separate delivery from storage, and whether you can say what happens when the recipient is offline.
- Design a collaborative document editor like Google Docs.Whether you recognise concurrent editing as a conflict-resolution problem rather than a locking one.
- Design a least-recently-used cache with O(1) get and put.Whether you can combine two data structures to hit a bound neither reaches alone.
- Design a parking lot system.Whether you can turn a vague brief into a clean object model and resist inventing requirements.
The behavioural round
Tell a specific, true story with your own decisions in it, and let the result carry the point.
- Tell me about yourself.Whether you can select. This is a question about editing, not biography.
- Why are you interested in working here?Whether you did any homework, and whether your reason survives being swapped for a competitor.
- Describe a time when there was a conflict within your team. How did you handle it?Whether you can describe a disagreement without making the other person the villain.
- Tell me about a time you failed. How did you deal with it?Whether you can own a real failure without either minimising it or performing contrition.
The machine-learning round
Explain the mechanism, not the definition, and say when each technique stops working.
- What is gradient descent?Whether you can explain the mechanism and its failure modes rather than recite the update rule.
- What is regularization, why do we use it, and what are some common methods?Whether you connect it to the bias-variance trade-off rather than listing techniques.
- Explain principal component analysis.Whether you can give the geometric picture and say what PCA assumes.
- What is the vanishing gradient problem?Whether you can trace it to the chain rule and name the fixes that actually addressed it.
How these were chosen
Public question corpora nominate the questions that recur; first-hand reports from engineers corroborate them with a named company and a date. A question only ships if two independent sources attest it, or two separate people report being asked it. Every quote was re-fetched from its source and matched before it counted: 657 observations, 657 verified.
One honest caveat: the shortlist rests on two families of evidence rather than three. Company hiring pages, which would be the third, are mostly JavaScript applications this pipeline cannot read, so they contributed nothing. The behavioural and machine-learning questions have thinner evidence behind them than the coding ones.