Mercor technical phone screen interview

Questions Mercor asks in this round 17

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  Sorting complexity: beat O(n²), then design the worst correct sortCodingA verbal round with no coding, asked as a quick series: 1. Explain a sorting algorithm faster than O(n²) and why it is faster; be ready for quicksort's worst case. 2. Name or…

  Last asked Oct 2026Were you asked this too?
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  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 2026Were you asked this too?
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  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 2026Were you asked this too?
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  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 2026Were you asked this too?
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  Project deep dive: present a project you ledBehavioralPresent a project you led in about 20 minutes: context, your role, the architecture, three hard trade-offs, metrics, cost and return, and what you would change. Then take 25…

  Last asked Sep 2026Were you asked this too?
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  Check and insert among a million user IDsSystem designA service holds about a million user IDs. Each request carries a user ID: if it is not in the set yet, add it. Decide how to store the IDs and run this check-and-insert, and talk…

  Last asked Oct 2026Were you asked this too?
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  Probability that every coffee from one shop beats the other'sCodingTwo cups come from one coffee shop and two from another, and each cup's quality is an independent draw from one continuous distribution. How likely is it that the first shop's…

  Last asked Oct 2026Were you asked this too?
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  Design an API to deep-copy a dataset with its tasks, responses and gradesSystem designA dataset holds tasks, each task holds model responses, and each response holds grades. Design an API that copies a dataset with everything under it, so that the copy and the…

  Last asked Sep 2026Were you asked this too?
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  LLM application engineering: RAG, context limits, state and prompt injectionAI/ML designQuick conceptual questions for an applied AI engineer, each answered in a couple of minutes from real experience: 1. When would you use retrieval-augmented generation and when…

  Last asked Sep 2026Were you asked this too?
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  Shortest path in a grid with obstacle eliminationCodingA grid has empty cells and obstacles. Find the fewest steps from the top-left to the bottom-right cell moving up, down, left or right, when you may remove up to k obstacles along…

  Last asked Sep 2026Were you asked this too?
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  Design a project-to-contractor matching systemSystem designDesign a system that matches projects needing work done with contractors who can do it: how projects and contractor profiles are stored and indexed, how candidates are found and…

  Last asked Aug 2026Were you asked this too?
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  Design unique username registrationSystem designNew accounts pick a permanent username, and no two accounts may ever own the same name after normalization (case and similar rules). Design the registration service: a quick "is…

  Last asked Aug 2026Were you asked this too?
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  Design an analytics platform for external career dataSystem designExternal providers send snapshots and updates of people's career profiles. Design the data platform for an internal analytics team: - Backfilling and ingesting provider data…

  Last asked Jun 2026Were you asked this too?
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  Evaluate noisy data for LLM post-trainingAI/ML designYou have data collected for post-training a language model and some of it is noisy. How would you measure its quality, find the bad examples, and decide what to keep, fix or drop…

  Last asked May 2026Were you asked this too?
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  Design a news feedSystem designDesign the home feed for a social network with 1B users: posts from people you follow, ranked, fresh within seconds.

  Last asked May 2026Were you asked this too?
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  Build an eval harness for local models served by OllamaSystem designA take-home of about four hours (AI coding tools allowed): write an evaluation harness that runs a set of test cases against language models served locally through Ollama, scores…

  Last asked Mar 2026Were you asked this too?
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  Infrastructure fundamentals: networking, Kubernetes and streamingSystem designA rapid-fire round of around twenty short questions with no coding, for an infrastructure role. Reported ones: 1. What happens between typing a site's address in the browser and…

  Last asked Jan 2026Were you asked this too?