Mercor

48 engineering jobs

Prep for this company

22 questions

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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 2026
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 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
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 2026
Design a workflow orchestration systemSystem designUsers define a workflow as steps with dependencies, then start runs of it. Design the system that runs each step once its dependencies finish, records the state of every run and…
Last asked Sep 2026
Can every car park with preferred spots and forward-only overflowCodingA one-way street has n spots numbered 0 to n - 1. Cars arrive in order; car i wants spot preferencesi, takes it if free, and otherwise drives forward to the next free spot. A car…
Last asked Sep 2026
Explore a friend graph through a remote API with few callsCodingYou cannot read a social graph directly; the only access is getfriends(userid), a remote call that returns a user's friends and costs a network round trip. Write code that…
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
Exchange rate between two currencies through chained conversionsCodingYou get a list of rates from, to, rate, each meaning one unit of from is worth rate units of to. Given a source and a target currency, return the rate between them by chaining…
Last asked Sep 2026
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 2026
LLM application engineering: RAG, context limits, state and prompt injectionML 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 2026
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 2026
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 Aug 2026
Design a ticket booking systemSystem designSell seats for concerts and games where demand spikes the moment sales open: hold seats briefly, never sell one twice, and stay up under the rush.
Last asked Jul 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
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 May 2026
Evaluate noisy data for LLM post-trainingML 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 2026
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 2026
Design candidate search for a talent marketplaceML designDesign a system that lets a company search for candidates and ranks them for a role: how candidate profiles are represented and indexed, how a query or job description retrieves…
Last asked May 2026
Referral networkCodingImplement a referral network: users refer other users, and the network records who referred whom. Support adding referrals and answering questions about a user's referrals, such…
Last asked May 2026
Build an eval harness for local models served by OllamaAI systemA 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 2026
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 2026