Mercor interview questions

Showing 31–44 of 44 results

• Implement a Referral NetworkMedium

  Design and implement an in-memory referral network as a directed acyclic graph (DAG) supporting cycle-safe edge insertion, depth-bounded reachability queries, and expected reward computation under geometric decay.

  MercorMachine Learning EngineerCoding & AlgorithmsOnsite
• Make a Charge-Then-Record Payment Endpoint Safe Against Timeouts, Retries and CrashesMedium

  A payment endpoint calls an external provider to charge the customer and then writes a record to its own database. The question asks what can go wrong and how to redesign the flow, testing failure analysis for crashes and timeouts, safe retries, durable payment state, recovery through status checks, webhooks and reconciliation, and lock placement.

  MercorSoftware EngineerSystem DesignTechnical Screen
• Make a Dict-Based Memoization Cache Safe for Concurrent ThreadsMedium

  A memoization cache built on a plain Python dictionary wraps an expensive function and is now called from many threads at once. The question asks what goes wrong and how to fix it, testing race-condition analysis, lock scope and its throughput cost, duplicate-work prevention, and exception handling for waiting callers.

  MercorSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Probability Both Drinks from One Coffee Shop Outscore Both Drinks from AnotherMedium

  A probability brainteaser: two drinks are ordered at each of two coffee shops and every drink receives a quality score, and you must find the probability that both drinks from the first shop outscore both drinks from the second. It tests symmetry arguments, counting rankings, and stating independence and tie assumptions.

  MercorSoftware EngineerStatistics & MathTechnical Screen
• Probability That One Customer's Two Coffees Beat Another's TwoMedium

  A probability puzzle in which two customers each buy two cups of coffee of random quality, and you find the chance that one customer's cups are better than the other's. It tests clarifying what better means, using symmetry over rankings, checking the result a second way, and reasoning about ties and correlated cups.

  MercorSoftware EngineerStatistics & MathTechnical Screen
• Project Deep Dive With Product-Level Probing, AI Tool Use, and Startup MotivationMedium

  A startup background round: introduce yourself, walk through a recent project probed from a product angle (who owns each decision, what done means, success metrics), explain what the company does and why you want to join, and describe your side project. It also tests how you use AI tools for on-call automation, code review, and design discussions.

  MercorSoftware EngineerBehavioral & LeadershipTechnical Screen
• Reason About Coffee-Quality Comparison ProbabilitiesMedium

  Calculate conditional comparison probabilities for coffee quality scores under continuous and discrete distributions, accounting for ties and sample permutations.

  MercorSoftware EngineerStatistics & MathTechnical Screen
• Review a Compact GPT-Style Transformer ImplementationMedium

  Assess and debug a compact decoder-only Transformer implementation. Candidates trace tensor dimensions through causal multi-head self-attention, identify flaws in next-token loss alignment and KV-cached generation, and establish equivalence between cached and uncached forward passes.

  MercorMachine Learning EngineerMachine LearningOnsite
• Review a Hand-Rolled Python CSV Serializer for Correctness and Performance BugsMedium

  A code review question on a short Python function that turns a table of rows into CSV text. Candidates must find its correctness and performance problems and write a fixed version, which tests delimiter handling, string building in Python, non-string cells, CSV quoting and escaping rules, and how to verify the fix.

  MercorSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Review an Asynchronous Cache for Races, Memory Growth, and Thread SafetyHard

  Tests understanding of asynchronous race conditions, memory leaks, and eviction in single-threaded event loops versus multithreaded synchronization in languages like C++.

  MercorSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Shortest Grid Path with Obstacle EliminationsMedium

  This question tests your ability to apply Breadth-First Search (BFS) on an augmented state space where path state includes both coordinates and remaining resources.

  MercorSoftware EngineerCoding & AlgorithmsTechnical Screen
• Sorting Complexity: Beating O(n^2), Quicksort's Worst Case, and a Slower SortMedium

  A verbal sorting-theory discussion: explain how to sort faster than quadratic insertion sort, identify quicksort's worst case, count the non-empty subsequences and the permutations of an n-element array, and design a correct sort that is deliberately slower than O(n^2). It tests asymptotic analysis, recurrence reasoning, and basic combinatorics.

  MercorSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Stripe Payment Integration: Error Handling, Idempotent Retries and Payment StorageMedium

  Explain how to add a Stripe payment integration to a backend service: how to handle errors and retries without charging a customer twice, what payment data to store, and which database to use given ACID and availability needs. Tests idempotency, failure handling, and data modeling for payments.

  MercorSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• The Worst Possible Sorting Algorithm and How to Enumerate Every PermutationMedium

  A verbal algorithms question: name the worst sorting algorithm that still always sorts correctly, analyze its running time, and explain how you would compute every permutation of the input exactly once. It tests reasoning about factorial complexity and knowledge of permutation enumeration methods.

  MercorSoftware EngineerSoftware Engineering FundamentalsTechnical Screen