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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

← Block

Senior Backend at Block

BackendSeniorOutcome unknown◆ Commonly asked· 2023

A senior backend loop. Balanced across coding, design, and collaboration.

The loop · 6 rounds

01

Round 01 · 3 questions

DSA / Coding

Data structures & algorithms on a whiteboard or shared editor.

  • Subtree of another tree.
    SeniorEasy◆ Commonly asked
    #tree#dfs
    PracticeLeetCode↗GeeksforGeeks↗
  • Serialize and deserialize a binary tree.
    SeniorHard◆ Commonly asked
    #tree#dfs
    PracticeLeetCode↗GeeksforGeeks↗
  • Longest consecutive sequence.
    SeniorMedium◆ Commonly asked
    #hashmap#array
    PracticeLeetCode↗GeeksforGeeks↗
02

Round 02 · 2 questions

Machine Coding

Build a working component or service under time pressure.

  • Build a file-upload service with chunking and resume.
    SeniorHard◆ Commonly asked
    #streaming#storage
    PracticeGeeksforGeeks↗Search↗
  • Build a REST endpoint with pagination, filtering and sorting.
    SeniorMedium◆ Commonly asked
    #api#pagination
    PracticeGeeksforGeeks↗Search↗
03

Round 03 · 2 questions

System Design

High-level architecture of a large-scale system.

  • Design a webhook delivery system with retries.
    SeniorMedium◆ Commonly asked
    #reliability#queues
    PracticeGeeksforGeeks↗Search↗
  • Design a multi-tenant SaaS data model.
    SeniorHard◆ Commonly asked
    #multi-tenancy#databases
    PracticeGeeksforGeeks↗Search↗
04

Round 04 · 3 questions

Tech Deep-Dive

Deep questions on your core stack and fundamentals.

  • How do circuit breakers and bulkheads improve resilience?
    SeniorMedium◆ Commonly asked
    #reliability
    PracticeGeeksforGeeks↗Search↗
  • What is backpressure and how do you handle it?
    SeniorHard◆ Commonly asked
    #streaming#reliability
    PracticeGeeksforGeeks↗Search↗
  • How does a write-ahead log guarantee durability?
    SeniorHard◆ Commonly asked
    #databases
    PracticeGeeksforGeeks↗Search↗
05

Round 05 · 1 question

Hiring Manager

Scope, ownership, and role-fit discussion with the manager.

  • How do you measure the success of a project after launch?
    Senior◆ Commonly asked
    #metrics
06

Round 06 · 2 questions

Behavioral / HR

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

  • When did you change your mind after seeing new evidence?
    Senior◆ Commonly asked
    #judgment#star
  • Tell me about the hardest bug you have debugged.
    Senior◆ Commonly asked
    #debugging#star

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