#code review

10 code review interview questions, asked at Mercor, Microsoft, Airbnb and 4 more companies. Last asked Oct 2026.

Make a charge-then-record payment flow safe against crashes and retriesCodingA backend first charges a customer through an external payment provider and then writes the payment to its own database. You are shown code like this (in Java or Python) and asked…
Last asked Oct 2026
Review a CSV-building function for correctness and performance bugsCodingYou are shown a short function (in Java or Python) that turns a table, a list of rows of string cells, into CSV text by appending to a string in a loop. Say what is wrong with its…
Last asked Oct 2026
Review a feature pipeline pull request, then serve features by freshnessML designYou are shown a pull request that changes a feature pipeline: the code that turns raw events into model features. All its tests pass. Review it live and explain what could go…
Last asked Sep 2026
Find the bugs in a dictionary memoization cache under concurrencyCodingA slow function is wrapped by a module-level dictionary that stores its results: look up the key, otherwise compute and store. You are shown the code and asked what breaks in…
Last asked Sep 2026
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Review a series of pull requestsCodingYou get two or three pull requests, each harder than the last, in Python or Java. Read each one, leave comments as you would on a real review, and point out bugs, design problems…
Last asked Aug 2026
Review a compact GPT-style transformer implementationML designYou are given a short implementation of a GPT-style decoder-only transformer. Read it and review it: explain what each part does (embeddings, attention with its causal mask…
Last asked Jul 2026
Find the bugs in an AI-generated URL shortenerCodingYou are handed a URL shortener that an AI assistant wrote. Read it, find what is wrong (correctness, collisions, validation, concurrency) and fix it, explaining each problem. Only…
Last asked Jun 2026
Build a hash map, make it thread-safe, and review a producer-consumer queueCodingImplement a hash map from scratch: hashing, buckets, collisions, resizing and the edge cases (null keys, rehashing while iterating). Then make it safe for many threads and discuss…
Last asked Apr 2026
Design a code review agentAI system designDesign an AI agent that reviews pull requests: it reads the diff and the surrounding code, leaves comments on bugs, risky changes and style problems, and may suggest fixes. Cover…
Last asked Mar 2026
Debug a codebase then propose long-term fixesCodingYou inherit a small order service: an inventory that holds stock for orders, a pricing module, and the order service that ties them together. Support tickets say stock…