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Technical Interviews: What I Wish I Knew Earlier

CareerInterviews

After 50+ technical interviews (both sides of the table), here’s what actually matters.

The Interview Loop

  1. Phone Screen (30 min): Coding basics
  2. Technical Round 1 (60 min): Data structures & algorithms
  3. Technical Round 2 (60 min): System design
  4. Behavioral (45 min): STAR method
  5. Final Round (30 min): Culture fit

Coding Interviews

What They’re Really Testing

  • Can you write working code?
  • Can you communicate your thought process?
  • Can you handle ambiguity?
  • Can you optimize?

The Framework

1. Clarify requirements (5 min)
2. Discuss approach (5 min)
3. Code solution (30 min)
4. Test and optimize (10 min)

Example Problem

Question: “Find two numbers in an array that sum to a target.”

Bad Response:

# Just start coding
for i in range(len(arr)):
    for j in range(i+1, len(arr)):
        if arr[i] + arr[j] == target:
            return [i, j]

Good Response:

Me: "Can the array have duplicates?"
Interviewer: "Yes"

Me: "Should I return indices or values?"
Interviewer: "Indices"

Me: "Can I use extra space?"
Interviewer: "Yes"

Me: "I'll use a hash map. Time O(n), space O(n)."
[Then code the solution]

System Design Interviews

The Framework

1. Requirements (10 min)
   - Functional: What features?
   - Non-functional: Scale? Latency?

2. High-level design (15 min)
   - Draw boxes and arrows
   - Identify components

3. Deep dive (25 min)
   - Database schema
   - API design
   - Scaling bottlenecks

4. Trade-offs (10 min)
   - CAP theorem
   - Consistency vs availability

Example: Design Twitter

Requirements:

  • 300M users
  • 100M daily active
  • 500M tweets/day
  • Read-heavy (100:1 read/write ratio)

High-Level:

Client → Load Balancer → API Servers → Cache → Database
                                      ↓
                                   Message Queue → Timeline Service

Deep Dive:

  • Database: PostgreSQL for users, Cassandra for tweets
  • Cache: Redis for timelines
  • CDN: For media files
  • Sharding: By user ID

Behavioral Interviews

STAR Method

Situation: Set the context Task: What needed to be done Action: What you did Result: What happened

Example:

Question: “Tell me about a time you had a conflict with a teammate.”

Bad: “We disagreed about architecture. I convinced them I was right.”

Good: “Situation: We were building a microservices system. My teammate wanted to use REST, I preferred gRPC.

Task: We needed to decide quickly to meet our deadline.

Action: I proposed we prototype both approaches over a weekend. We measured latency, throughput, and developer experience.

Result: gRPC was 3x faster but harder to debug. We chose REST for the MVP, documented gRPC as a future optimization. The team appreciated the data-driven approach.”

Common Mistakes

  1. Not asking questions - Always clarify requirements
  2. Jumping to code - Discuss approach first
  3. Staying silent - Think out loud
  4. Giving up - Ask for hints
  5. Not testing - Walk through examples

Preparation Tips

For Coding

  • LeetCode: 150 problems (Easy: 50, Medium: 80, Hard: 20)
  • Focus on patterns: Two pointers, sliding window, DFS/BFS
  • Practice on a whiteboard or Google Doc (not IDE)

For System Design

  • Read “Designing Data-Intensive Applications”
  • Study real systems: Twitter, Netflix, Uber
  • Practice drawing diagrams

For Behavioral

  • Prepare 5-7 STAR stories
  • Cover: leadership, conflict, failure, success
  • Practice out loud

The Day Of

  • Sleep well - More important than last-minute cramming
  • Arrive early - 15 minutes buffer
  • Ask questions - Shows engagement
  • Be honest - “I don’t know, but here’s how I’d figure it out”
  • Follow up - Send thank-you email within 24 hours

Red Flags (From Interviewer Side)

  • Arrogant or dismissive
  • Can’t explain past work
  • Blames others for failures
  • Doesn’t ask any questions
  • Gives up easily

Conclusion

Interviews are a skill. Practice makes perfect.

Key Takeaways:

  • Clarify before coding
  • Communicate your thought process
  • Use frameworks (STAR, system design)
  • Practice consistently
  • Be yourself

What interview question stumped you? Share your experience!

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