91 Mock Coding Interviews with Tough Tongue AI

Back in my final year of undergrad, I was grinding LeetCode problems daily for hours, thinking that was enough. Then my friends and I started doing mock interviews—and that’s when I realized the hardest part wasn’t solving problems, it was explaining my thinking under pressure.

Those peer sessions taught me everything, but they were a nightmare to coordinate. Friends would get bored after 20 minutes, didn’t know optimal solutions, or couldn’t give useful feedback. Also, none of us had been on the other side of the interview table.

Fast forward—I’m incredibly grateful to those friends who stuck through those grueling practice sessions with me. Their patience and support helped me land my dream job at Meta in 2016. But I knew there had to be a better way for future candidates.

That’s why we built 91 AI-powered coding interview scenarios that mirror actual interviews at top tech companies. It’s like having that patient, knowledgeable friend available 24/7—with real-time code execution and instant feedback.

Here’s our 21-Days-30-Problems-Challenge: We’ve curated 30 strategically chosen problems that cover 80% of all interview patterns. Your mission, should you choose to accept it, is to master these problems in just 21 days. Scroll down to see the complete list and boost your interview readiness.

Practicing with Tough Tongue AI

Tough Tongue AI provides the most realistic coding interview practice available. Our AI interviewer conducts dynamic conversations, executes your code in real-time, and provides instant feedback—just like interviewing with a senior engineer at a top tech company. Notable features:

• Hyper-Realistic Interviews: Our AI doesn’t just present problems—it engages in natural conversations, asks clarifying questions, provides hints when you’re stuck, and guides you through complex solutions.

• Code Execution: Write code in Python, Java, C++, or JavaScript. Our AI runs your code, catches bugs, and suggests optimizations in real-time.

• 24/7 Availability: Practice anytime, anywhere. No scheduling required, no human coordination needed.

• Adaptive Learning: The AI personalizes your experience based on your performance, focusing on areas that need improvement while building your confidence.

Full Collection of 91 AI Interview Scenarios

We’ve organized our comprehensive coding interview scenarios into difficulty-based collections with links below. You can explore our full collection anytime. Also, we are constantly adding new scenarios.

However, whether your a fresh grad or a senior engineer looking for a new role, we recommend you to start with the strategic 21-days-30-problems-challenge below & then come back picking up a random problem from the full collection.

Easy Questions | Medium Part I | Medium Part II | Hard Questions

The 21-Day-30-Problem Challenge

We challenge you to complete the following curated list of 30 problems in 21 days. These questions are divided into categories / patterns. These questions cover the 80% of the patterns that you will see in the interviews. Follow the approach below for the best results:

1. Practice 2-5 problems per category to learn the core patterns
2. Switch to a different category to avoid tunnel vision
3. Come back to random problems once you’ve covered all categories
4. Focus on pattern recognition rather than memorizing solutions

The Top 30 Must-Practice Problems

📊 Arrays & Hash Tables (9 problems)

1. Find the Perfect Pair - Two Sum (fundamental pattern)
2. Triple Zero Hunt - 3Sum (two pointers)
3. Array Deduplication Challenge - Remove duplicates (in-place)
4. The Missing Positive Hunt - First missing positive
5. Peak Subarray Sum - Maximum subarray (Kadane’s)
6. Interval Fusion Challenge - Merge intervals
7. Matrix Spiral Traversal - Spiral matrix
8. Power Set Generator - Generate subsets
9. The Pivot Hunt Challenge - Search rotated array

🔤 String Manipulation (7 problems)

10. Unique Character Window Finder - Longest substring without repeating
11. Mirror String Hunter - Longest palindromic substring
12. Balanced Parentheses Generator - Generate parentheses
13. Bracket Balance Checker - Valid parentheses
14. Pattern Wizard: Advanced String Matching - Regular expression matching
15. The Smallest Window Hunt - Minimum window substring
16. String Transformation Challenge - Edit distance

🔗 Linked Lists (5 problems)

17. Linked List Arithmetic: Sum of Reversed Numbers - Add two numbers
18. Eliminate the Nth Node from List’s Tail - Remove nth from end
19. Combine Sorted Linked Lists - Merge two sorted lists
20. The Great List Unification Challenge - Merge k sorted lists
21. Circular Shift Challenge - Rotate list

🌳 Trees & Dynamic Programming (5 problems)

22. Tree Walker: Inorder Journey - Binary tree inorder traversal
23. Binary Tree Twin Detector - Same tree
24. The Stairway Challenge - Climbing stairs
25. Robot Grid Navigator - Unique paths
26. Treasure Hunt: Finding the Cheapest Path - Minimum path sum

🔄 Backtracking & Advanced (4 problems)

27. Target Sum Builder - Combination sum
28. The Ultimate Puzzle Master - Sudoku solver
29. Letter Grid Explorer - Word search
30. Water Tank Maximizer - Container with most water

🗓️ Your 21-Day Roadmap

Days 1-7: Arrays & Hash Tables Foundation (Problems 1-9)

• Build foundational patterns that appear in 40% of interviews | Goal: 1-2 problems daily | Time: 1-2 hours daily

Days 8-14: String Mastery (Problems 10-16)

• Conquer sliding window and string algorithms | Goal: 1 problem daily | Time: 1-2 hours daily

Days 15-19: Linked Lists & Trees (Problems 17-26)

• Master pointer manipulation and tree traversals | Goal: 2 problems daily | Time: 1.5-2 hours daily

Days 20-21: Advanced Patterns + Review (Problems 27-30)

• Tackle backtracking and advanced algorithms + review key patterns | Goal: 2 problems daily + review | Time: 2-3 hours daily

My Recommendations for Coding Interviews

After going through hundreds of interviews myself and helping others land roles at top tech companies, here’s what I’ve learned actually matters:

Talk through your thinking out loud: I used to think the code was everything, but interviewers care more about your thought process. When I started verbalizing my approach—even when I wasn’t sure—my interview performance improved dramatically. They want to see how you break down problems, not just if you know the answer.

Get something working first, optimize later: This was a game-changer for me. I’d spend 20 minutes trying to find the perfect O(log n) solution and run out of time. Now I always start with the brute force approach that works, then improve it. Most interviewers appreciate this pragmatic thinking.

Ask clarifying questions early: I learned this the hard way after solving the wrong problem in a Meta interview. Now I always ask about edge cases, input constraints, and expected output format. It shows you’re thorough and prevents costly misunderstandings.

Walk through test cases: I make it a habit to trace through my solution with the given examples before saying I’m done. Catching bugs during the interview shows good engineering instincts and attention to detail.

Recognize the underlying patterns: This is the most important advice I can give. Every problem in our 30-question list represents a category. After each practice session, ask yourself: “What pattern was this testing?” Once you see the patterns, interviews become much more predictable.

What you’ll achieve: Confidently tackle any coding interview, communicate clearly, and recognize patterns quickly in just 21 days. All 30 problems are available in our scenario collections above, each with AI interviewer and instant feedback.

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Appendix: The Typical 45-Minute Coding Interview Flow

Most coding interviews follow a predictable 4-phase structure:

• Phase 1 (Minutes 1-10): Problem Setup & Clarification Understand the problem and ask clarifying questions about constraints and edge cases

• Phase 2 (Minutes 10-20): Approach & Strategy Discuss your approach, walk through examples, and refine your solution strategy

• Phase 3 (Minutes 20-40): Code Implementation Write clean, readable code while thinking aloud and handling edge cases. (On Tough Tongue AI platform, you can run your code in real-time)

• Phase 4 (Minutes 40+): Follow up questions & Wrap-up The interviewer will ask follow-up questions and wrap up the interview.