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Interview Preparation Playbook – SDE-II Backend

Goal of this file: Give you a repeatable process for mock interviews, revision, and polishing your performance as an SDE-II backend candidate.

1. Mock Interview Structure​

  • Recommended Weekly Routine (Final 4–6 Weeks)

    • 2× Coding + DSA sessions (60 min each)
    • 2× Machine Coding / LLD sessions (90–120 min each)
    • 2× System Design sessions (60–75 min each)
    • 1× Behavioral / Resume walkthrough (45–60 min)

  • Coding + DSA Mock (60 min)

    • 5–10 min: clarify problem, discuss examples.
    • 30–40 min: implement solution.
    • 5–10 min: test and optimize.
    • 5–10 min: complexity analysis and discussion.

  • Machine Coding / LLD Mock (90–120 min)

    • 10–15 min: clarify requirements, identify constraints.
    • 15–20 min: design APIs, classes, DB schema.
    • 45–60 min: implement core flows in Node.js/TypeScript.
    • 10–15 min: tests & edge cases, extensions.

  • System Design Mock (60–75 min)

    • 5–10 min: clarify requirements, define scope.
    • 10–15 min: high-level component diagram.
    • 15–20 min: deep dive on 2–3 critical components (DB, cache, queues).
    • 10–15 min: bottlenecks, scaling strategies, trade-offs.
    • 5–10 min: recap and Q&A.

2. 7-Day Final Revision Plan (Before Interviews)​

Assume you have already completed most of the 16-week roadmap; this plan is for tight revision.

  • Day 1 – JS/TS + Node Foundations

    • 1–2 hours: Review JS/TS notes (closures, prototypes, async, TS advanced types).
    • 1–2 hours: Review Node internals, middleware, error handling, logging examples.
    • Mock: 1x coding round (arrays/strings + hash maps).

  • Day 2 – Databases & Caching

    • 1–2 hours: Review MongoDB/MySQL indexing, normalization, transactions.
    • 1–2 hours: Redis basics, caching strategies, rate limiting.
    • Mock: Design + sketch a simple data model for a notification or chat service.

  • Day 3 – System Design (APIs + Service Design)

    • 2–3 hours: Walk through at least 2 design problems:
      • e.g., Notification system, Rate limiter service.
    • Focus on:
      • API surface.
      • Storage choices.
      • Caching and queues.

  • Day 4 – Machine Coding

    • 3–4 hours: Do 1–2 full machine coding problems from machine-coding-bank.md.
    • Time-box:
      • 15 min design
      • 60–75 min implementation
      • 15–20 min tests + refactor

  • Day 5 – DSA & Theory

    • 2 hours: 4–6 mixed DSA problems (arrays/strings/trees/graphs).
    • 1–2 hours: Review theory-round.md (OS, networking, DBMS, CAP/ACID/BASE).

  • Day 6 – System Design + Behavioral

    • 2 hours: 1–2 system design mocks (Uber-like + file storage service).
    • 1 hour: Behavioral prep (see below).

  • Day 7 – Light Review & Rest

    • Skim notes, pattern cheat sheets, design diagrams.
    • No heavy new practice; aim to be fresh.

3. 1-Month Polishing Plan​

Follow after completing most of the core roadmap; this is for converting knowledge to performance.

  • Week 1

    • Focus on weakest coding areas (from your notes).
    • 3–4 DSA sessions + 1 machine coding session + 1 small system design session.

  • Week 2

    • Focus on system design:
      • 3 system design sessions.
      • 1–2 machine coding sessions.
      • 2–3 DSA sessions.

  • Week 3

    • Mixed practice:
      • 2 DSA, 2 system design, 2 machine coding, 1 theory/behavioral session.
    • Start timed mocks (as if real interviews).

  • Week 4

    • Full interview simulations:
      • 2× DSA + 2× System design + 2× Machine coding + 1× Behavioral.
    • Focus on:
      • Clear communication.
      • Not over-engineering.
      • Finishing within time.

4. Common Mistakes Candidates Make​

  • Coding

    • Jumping into code without clarifying the problem.
    • Not discussing time/space complexity.
    • Poor naming, no modularization (everything in main or one function).

  • Machine Coding

    • Over-engineering: building full frameworks instead of solving the core problem.
    • Ignoring edge cases and error handling (invalid input, missing data).
    • Not thinking about extensibility (adding a new vehicle type, new notification channel).

  • System Design

    • Listing buzzwords (Kafka, Redis, Kubernetes) without explaining why.
    • Diving into database schema too early without defining APIs and flows.
    • Ignoring bottlenecks, back-of-the-envelope estimates, and failure modes.

  • Behavioral

    • Giving generic answers without specific examples.
    • Blaming others instead of owning mistakes and learnings.
    • Not tying experiences back to impact (metrics, performance, reliability).

5. What Interviewers Expect from SDE-II​

  • Technical

    • Solid fundamentals, not necessarily perfection in DSA.
    • Clear thinking, trade-off awareness.
    • Real-world understanding of production issues (timeouts, retries, failures).

  • Ownership

    • Evidence that you own features/services, not just tasks.
    • You can drive a project from requirements to production.

  • Communication

    • You explain your thought process.
    • You listen to hints and adapt.
    • You can say "I don’t know" and then reason logically from first principles.

Use this playbook as a checklist in the final 4–6 weeks; combine it with the day-wise and week-wise plans.