Top mistakes on LeetCode interview questions for FAANG

If you're aiming for a FAANG offer, chances are you've been grinding away at LeetCode problems. But raw effort isn’t enough. Too often, candidates practice inefficiently, build bad habits, and plateau before they reach the interview stage.

In this blog, we'll break down the most common mistakes developers make when working through LeetCode interview questions—and how you can avoid them to maximize your chances of landing that dream role.

Mistake 1: Prioritizing quantity over quality#

It’s tempting to treat LeetCode like a numbers game—"If I solve 300 problems, I’ll be ready." But solving problems without understanding the underlying patterns is wasted effort. High-frequency practice without feedback loops eventually leads to stagnation and burnout.

Focus on depth, not just volume:

• Reflect on why your solution worked (or didn’t) and what trade-offs you made.

• Identify the pattern behind the problem (e.g., sliding window, binary search).

• Write a second, cleaner version of your solution after you fully understand it.

• Focus on solving problems without relying on hints, to simulate interview conditions.

Mastery of LeetCode interview questions requires thoughtful repetition, focused problem sets, and an emphasis on quality problem-solving skills.

Mistake 2: Ignoring time and space complexity#

Too many candidates get a working solution and immediately move on. In real FAANG interviews, interviewers care deeply about the efficiency of your solution. A brute-force solution might be acceptable early in your prep, but you need to aim higher by the time you interview.

Make it a habit to:

• Analyze time complexity (best, average, worst case) after every solution.

• Discuss space complexity and identify opportunities to optimize it.

• Proactively suggest improvements even if your initial code works fine.

• Practice optimizing algorithms (e.g., moving from O(n^2) to O(n log n)).

Practicing this consistently during LeetCode sessions makes it second nature in interviews and helps you stand out from the average candidate.

Mistake 3: Only practicing easy and medium problems#

Easy wins feel good, but FAANG tech interviews rarely focus on "easy" questions. Most LeetCode interview questions you’ll encounter in real interviews fall into Medium or Hard difficulty.

Structure your prep to include:

• At least 30–40% Medium problems.

• Regular exposure to Hard problems (even if you don't solve them fully).

• Deep dives into solutions for problems you can’t crack—study and reimplement.

Challenging yourself with harder problems trains your ability to deal with unfamiliar scenarios—a key skill at FAANG companies, where ambiguous problems are the norm.

Mistake 4: Memorizing solutions instead of building intuition#

Some candidates "brute-force" their prep by memorizing solutions and code snippets. While this might help you recognize similar problems, it won't help you solve new variants under pressure.

Instead:

• Focus on recognizing problem patterns, not problem IDs.

• Practice explaining why each solution works out loud to a peer or rubber duck.

• Rebuild solutions from scratch days later to test your retention and intuition.

• Solve variations of the same problem to solidify your pattern recognition.

Deep understanding lets you adapt known techniques to solve new, unseen LeetCode interview questions—exactly the kind of agility top companies look for.

Mistake 5: Skipping mock interviews#

Practicing alone is valuable, but it’s not enough. Mock interviews simulate the stress, communication, and time constraints of real FAANG interviews.

You should:

• Schedule regular mock interviews with peers, mentors, or online platforms.

• Practice thinking aloud and explaining your logic clearly from start to finish.

• Get used to handling hints, partial success, and course corrections professionally.

• Record and review mock interviews to spot communication and thinking gaps.

Mock interviews teach resilience, flexibility, and clear thinking under pressure—skills that grinding LeetCode alone cannot.

Mistake 6: Underestimating behavioral questions#

While most candidates obsess over coding rounds, they often neglect behavioral interviews. FAANG companies evaluate not just your technical skills, but also your problem-solving approach, resilience, and communication style.

Tips:

• Prepare STAR (Situation, Task, Action, Result) stories for leadership principles.

• Connect your LeetCode practice to soft skills (e.g., perseverance, iteration).

• Reflect on projects or learning experiences where you overcame obstacles.

• Treat behavioral rounds with the same rigor you apply to coding prep.

Behavioral excellence can often be the deciding factor between two equally strong technical candidates.

Mistake 7: Practicing without feedback loops#

Feedback accelerates learning. Simply solving a problem isn’t enough—you need to understand how your approach could be better.

Effective feedback loops:

• Review top-rated solutions and compare multiple approaches.

• Analyze code efficiency and readability after each session.

• Maintain a mistake log to track recurring errors and weaknesses.

• Spend time each week reflecting on growth areas.

Without regular reflection, you risk plateauing and reinforcing bad habits that could hurt you in a real FAANG interview.

Mistake 8: Neglecting edge cases#

One of the quickest ways to fail LeetCode interview questions at FAANG is missing edge cases. Interviewers love to ask "What happens if the input is empty?" or "What if the array is sorted in reverse?"

Train yourself to:

• Test small, large, and special inputs systematically.

• Always ask clarifying questions about problem constraints and assumptions.

• Develop a checklist of common edge cases by data structure and algorithm.

• Proactively brainstorm edge cases before writing code.

Handling edge cases gracefully shows you're not just coding—you’re engineering reliable, scalable solutions.

Mistake 9: Not mastering fundamental data structures#

Before you dive into complex problems, you must have an iron grip on basic data structures:

• Arrays and Strings

• Linked Lists

• HashMaps and HashSets

• Trees and Graphs

• Heaps, Stacks, and Queues

Every solution is built on these foundations. Weakness here will cost you even on Medium-level LeetCode interview questions. Revisit the basics regularly, build utilities from scratch, and understand the trade-offs of each structure.

Mistake 10: Rushing into coding without a plan#

In interviews, jumping straight into coding is risky. FAANG interviewers expect you to:

• Discuss your high-level approach and options first.

• Sketch the solution outline or pseudo-code before writing.

• Highlight potential pitfalls and optimization ideas upfront.

Planning demonstrates organized thinking, foresight, and communication skills—critical traits for engineering roles at top companies. Practice structured problem-solving until it becomes second nature.

Mistake 11: Ignoring System Design questions at mid-level roles#

If you're interviewing for L4+ roles (Mid-level, Senior Engineer), don't make the mistake of only practicing coding questions. System Design often shows up earlier than people expect.

Prep basics like:

• Designing a URL shortener, message queue, or file storage service.

• Load balancing strategies and high-availability design.

• Scaling read-heavy and write-heavy services.

• Fault tolerance, replication, and sharding fundamentals.

Even a lightweight system design discussion can make or break your FAANG interview outcome. Build intuition early by studying real-world system architectures.

Final thoughts#

Cracking LeetCode interview questions is about smart, structured, and reflective practice—not just grinding out hundreds of problems. Avoiding these common mistakes can save you countless hours and dramatically improve your readiness for FAANG interviews.

Remember: quality over quantity, intuition over memorization, and practice under real-world conditions. Focus on becoming a thoughtful, adaptable problem solver—not just a LeetCode machine.

Stay disciplined. Stay curious. And most importantly, stay reflective.

Happy interviewing!