How to Ace Technical Interviews: Developer & Engineer Guide
December 28, 2025 11 min read NextWalkin Blog
For a developer or engineer role, the technical round is where the job is genuinely won or lost — everything else is secondary. But 'technical interview' means very different things depending on where you're applying. A TCS or Infosys walk-in is not an Amazon coding round, and preparing for the wrong one wastes weeks. This guide covers what each actually tests, the fundamentals you can't skip, and how to prepare in a month without drowning.
In This Article
Know which kind of round you're walking into
The fundamentals you cannot skip
Learn the handful of patterns that cover most problems
How you solve matters as much as the answer
System design — only for mid-senior roles
A realistic one-month plan and the best resources
Know which kind of round you're walking into
IT-services walk-ins (TCS, Infosys, Wipro, Cognizant) usually run 20–30 minutes on fundamentals — OOP, DBMS, OS basics, and one language you can write on paper. They're testing that you understand core concepts, not that you can crack a hard DP problem. Product companies (Amazon, Google, and the well-funded startups) go deeper: 45–60 minute problem-solving on a shared editor, plus system design for senior roles. Startups often prefer a practical test — fix a bug, build a small feature, or a take-home. Figure out which bucket your target falls in before you plan your prep, because they reward different things.
The fundamentals you cannot skip
Whatever the format, be genuinely comfortable with the core data structures — arrays and strings, linked lists, stacks and queues, hash maps, trees, and at least basic graphs and heaps. For each, you should know what it is, when you'd reach for it, and the time complexity of its common operations. That last part matters most: nearly every coding question really begins with 'what's the right data structure here?', and picking well is half the solution. Don't just memorise code you've seen — understand why one structure beats another for a given problem.
Pro Tip: If your target is IT-services walk-ins, weight your prep toward OOP, DBMS (joins, normalisation, indexing) and OS basics over hard algorithms — that's what actually gets asked there.
Learn the handful of patterns that cover most problems
Coding questions look infinite but mostly reuse a few patterns: two pointers, sliding window, binary search, BFS/DFS on trees and graphs, and — for tougher rounds — dynamic programming, backtracking, and greedy. Learn two or three classic problems per pattern rather than grinding hundreds randomly. Once you can recognise 'this is a sliding-window problem' in the first minute, the solution stops being a puzzle and becomes a template you adapt. Pattern recognition, not raw problem count, is what separates people who clear these rounds from people who don't.
How you solve matters as much as the answer
Interviewers are watching your process, so make it visible. Spend the first couple of minutes actually understanding the problem — ask clarifying questions ('can the array have duplicates?', 'how large can the input get?', 'should I handle empty input?'). Then think aloud: say why you're leaning toward a particular approach before you write a line. Outline the plan, confirm it, then write clean code with readable names. Finally, dry-run your solution on a sample and the obvious edge cases, and talk about the time and space complexity. A candidate who communicates a decent solution clearly often beats one who silently writes a perfect one.
System design — only for mid-senior roles
With three or more years of experience, expect a design discussion: design a URL shortener, a chat app, a news feed. Use a simple frame every time — clarify requirements, sketch a high-level architecture, then drill into components, data model, APIs, and how it scales. Know the vocabulary that comes up constantly: load balancing, caching (Redis), sharding, message queues (Kafka), monolith vs microservices, and rate limiting. At walk-ins this is rare, but even being able to cleanly diagram a system you actually built signals maturity. The best practice is to reverse-engineer things you use — how might UPI or Zomato be structured?
Pro Tip: Draw your designs on paper as you practise. Being able to sketch a clear architecture diagram under pressure is a learned motor skill, not something you absorb by reading.
A realistic one-month plan and the best resources
A workable month: week one, revise all the core data structures and solve a few easy problems daily; week two, drill the main patterns and go deep on one language; week three, add DP, backtracking, and greedy plus DBMS/OS revision; week four, do timed mock interviews and fix weak spots. For resources, Indian candidates get a lot from Striver's SDE Sheet on YouTube (genuinely one of the best free structured prep tracks), LeetCode's curated interview lists, and 'Cracking the Coding Interview' as a reference. For IT-services and campus-style prep specifically, PrepInsta and GeeksforGeeks' company-wise archives are worth the time. Consistency beats intensity — 90 focused minutes daily outperforms a weekend cram.
Key Takeaway
A technical interview isn't a memory test — it's a demonstration that you can think through a problem in a structured way, pick sensible tools, write clean code, and catch your own edge cases. Match your prep to the kind of company you're targeting, learn the patterns rather than grinding blindly, and above all keep talking through your reasoning in the room. Every round you don't clear sharpens the next one. Keep solving, and the offer follows.