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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.

CC BY-NC 4.0 · © 2026

← Sierra

Senior Backend at Sierra

BackendSeniorOffer◆ Commonly asked· 2025

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

The loop · 6 rounds

01

Round 01 · 3 questions

DSA / Coding

Data structures & algorithms on a whiteboard or shared editor.

  • Word search in a grid.
    SeniorMedium◆ Commonly asked
    #backtracking#grid
    PracticeLeetCode↗GeeksforGeeks↗
  • Regular expression matching.
    SeniorHard◆ Commonly asked
    #dp#string
    PracticeLeetCode↗GeeksforGeeks↗
  • Same tree.
    SeniorEasy◆ Commonly asked
    #tree
    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↗
  • Implement a bulk-upsert endpoint with validation.
    SeniorMedium◆ Commonly asked
    #api#validation
    PracticeGeeksforGeeks↗Search↗
03

Round 03 · 2 questions

System Design

High-level architecture of a large-scale system.

  • Design an object storage service like S3.
    SeniorHard◆ Commonly asked
    #storage#scale
    PracticeGeeksforGeeks↗Search↗
  • Design a chat/messaging backend with delivery guarantees.
    SeniorHard◆ Commonly asked
    #websocket#queues
    PracticeGeeksforGeeks↗Search↗
04

Round 04 · 3 questions

Tech Deep-Dive

Deep questions on your core stack and fundamentals.

  • Idempotency in APIs — why and how.
    SeniorMedium◆ Commonly asked
    #api-design#idempotency
    PracticeGeeksforGeeks↗Search↗
  • Explain optimistic vs pessimistic locking.
    SeniorHard◆ Commonly asked
    #databases
    PracticeGeeksforGeeks↗Search↗
  • How do you run a zero-downtime database migration?
    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 give difficult feedback to a peer?
    Senior◆ Commonly asked
    #leadership
06

Round 06 · 2 questions

Behavioral / HR

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

  • Tell me about a time you went above and beyond for a customer.
    Senior◆ Commonly asked
    #customer#star
  • Describe a time you had to deliver bad news.
    Senior◆ Commonly asked
    #communication#star

Practice each round across every company

  • DSA / Coding
  • Machine Coding
  • System Design
  • Tech Deep-Dive
  • Hiring Manager
  • Behavioral / HR

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