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Interview questions from top companies, mapped to the exact round they show up in. Prep for what you will actually face.

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Online AssessmentDSA / CodingMachine CodingLow-Level Design

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The Loop aggregates publicly shared interview experiences and curated commonly-asked questions, each labeled with its source. Not affiliated with any company listed.

MIT · © 2026

← Brex

Mid Backend at Brex

BackendMidOutcome unknown◆ Commonly asked· 2025

A mid backend loop. Fast-paced; expect follow-ups that push on depth.

The loop · 5 rounds

01

Round 01 · 3 questions

DSA / Coding

Data structures & algorithms on a whiteboard or shared editor.

  • Combination sum.
    MidMedium◆ Commonly asked
    #backtracking
    PracticeLeetCode↗GeeksforGeeks↗
  • Word ladder — shortest transformation sequence.
    MidHard◆ Commonly asked
    #bfs#graph
    PracticeLeetCode↗GeeksforGeeks↗
  • Pow(x, n).
    MidMedium◆ Commonly asked
    #math#recursion
    PracticeLeetCode↗GeeksforGeeks↗
02

Round 02 · 2 questions

Machine Coding

Build a working component or service under time pressure.

  • Implement an exponential-backoff HTTP client.
    MidMedium◆ Commonly asked
    #reliability
    PracticeGeeksforGeeks↗Search↗
  • Implement an idempotent "charge" endpoint.
    MidHard◆ Commonly asked
    #idempotency#payments
    PracticeGeeksforGeeks↗Search↗
03

Round 03 · 1 question

Low-Level Design

Object-oriented / low-level design of a focused module.

  • Design a booking/reservation system core.
    MidMedium◆ Commonly asked
    #oop#concurrency
    PracticeGeeksforGeeks↗Search↗
04

Round 04 · 3 questions

Tech Deep-Dive

Deep questions on your core stack and fundamentals.

  • Explain database indexing and when a query uses one.
    MidMedium◆ Commonly asked
    #databases#indexing
    PracticeGeeksforGeeks↗Search↗
  • Explain connection pooling and why it matters.
    MidMedium◆ Commonly asked
    #databases
    PracticeGeeksforGeeks↗Search↗
  • How does the OAuth 2.0 authorization-code flow work?
    MidMedium◆ Commonly asked
    #auth#security
    PracticeGeeksforGeeks↗Search↗
05

Round 05 · 2 questions

Behavioral / HR

Values, collaboration, and past-experience (STAR) questions.

  • Tell me about the hardest bug you have debugged.
    Mid◆ Commonly asked
    #debugging#star
  • Tell me about a time you went above and beyond for a customer.
    Mid◆ Commonly asked
    #customer#star

◆ This experience is composed from commonly reported questions for this role and level. Real, individually-shared interviews will be layered in over time.