How to Run Mock Coding Interviews by Yourself with LeetCode

You know you should do mock coding interviews. Everyone says:

“Practice with friends or use a paid mock interview platform.”

But maybe:

• Your friends are busy or at a different level.
• Paid platforms are too expensive.
• You feel awkward asking coworkers.

The good news: you can run surprisingly effective mock coding interviews by yourself using LeetCode, a timer, and a bit of structure.

This guide shows you how to design solo mock interviews that build real interview skills—not just problem-solving, but also pacing, communication, and stress management.

TL;DR

• Solo mock interviews are about simulating constraints: time limits, unfamiliar problems, no copy-paste from solutions, and clear verbal reasoning.
• The core workflow: pick a problem set, timebox the session, talk through your thinking, implement under a realistic constraint, and run a short retrospective afterwards.
• You can use LeetCode’s random problem features, custom lists, and tools like mock interview simulator to approximate a real interviewer.
• Beginners often “practice” by coding slowly with solutions open, which doesn’t mimic interview conditions and leads to a nasty surprise on interview day.
• With a repeatable solo-interview routine, you’ll build confidence, timing, and communication skills—even without another human on the call.

What a Real Coding Interview Actually Tests

It’s not just “can you solve the problem eventually?”

Interviewers look for:

• Problem understanding: Do you clarify requirements and constraints?
• Approach selection: Can you pick a reasonable pattern (two pointers, BFS, DP, etc.)?
• Communication: Do you explain your thinking clearly as you go?
• Implementation: Can you translate ideas into clean, working code under time pressure?
• Debugging: Do you test with edge cases and correct mistakes calmly?

Solo mock interviews should exercise all of these, not just the implementation part.

Step-by-Step: Designing a Solo Mock Interview Session

Step 1: Choose the right problem set

Pick:

• 1–2 Medium problems (or 1 Easy + 1 Medium if you’re early in prep).
• From topics you expect in interviews (arrays/strings, hash maps, trees/graphs, DP).

Options:

• Create a custom list on LeetCode with curated problems.
• Use a DSA learning path based on Blind 75 / Grind 75.
• Let a tool like LeetCopilot suggest problems at your current level.

Step 2: Set clear constraints

Decide:

• Time per problem (e.g., 35–40 minutes).
• No solution tab until time is up.
• No running code every 5 seconds—batch your tests thoughtfully.

Write it down:

Solo Mock Rules:
- 40 minutes maximum
- No editorial
- Explain thinking out loud
- 5-minute retrospective at the end

Step 3: Simulate the interview start

Treat the problem like an interviewer just read it to you:

1. Read the prompt once.
2. Restate it in your own words out loud.
3. Ask clarifying questions (to yourself, but verbally):
   • “Can the array be empty?”
   • “What are the size constraints?”
   • “Are elements sorted?”

This builds the habit you’ll use with a real interviewer.

Talking Through Your Thought Process (Even When Alone)

It feels silly at first, but narrating your reasoning is crucial.

What to say

• How you interpret constraints.
• What brute-force solution you see.
• Which pattern you’re considering and why.
• Trade-offs between approaches.

Example:

“A brute-force solution would check all pairs, which is O(n²). Since n can be 10^5, that’s too slow. The array is sorted, so I’m thinking two pointers from both ends to find a pair summing to target.”

If you’re using an AI-based mock interview simulator, it can respond to this reasoning and push back like a real interviewer.

Implementation: Coding Under a Timer

Step 1: Sketch before code

Spend 3–5 minutes:

• Writing a high-level plan in comments.
• Identifying key invariants or helper functions.

Example:

# Plan:
# 1. Use sliding window with hashmap of frequencies
# 2. Expand right, update counts
# 3. Shrink left while window has more than k distinct
# 4. Track max window length

Step 2: Implement steadily

Focus on:

• Clear variable names.
• Keeping functions small.
• Avoiding perfectionism—get something working, then refine if time allows.

Step 3: Test with hand-picked cases

Before pressing “Run”:

• Design 3–5 test cases by hand (edge cases + typical cases).
• Walk through them mentally or with quick prints.

This mirrors how strong candidates test in real interviews.

Retrospective: The 5-Minute Post-Interview Review

Once the timer ends—regardless of whether you solved it—do a quick retrospective:

1. Outcome: Solved? Needed hints? Ran out of time?
2. Pattern: Which pattern did the problem actually use?
3. Mistake: Where did you lose time or get stuck?
4. Next time rule: What will you do differently?

Example:

Outcome:
- Got to working solution at 38 minutes; minor bug with edge case.

Pattern:
- Sliding window for longest substring.

Mistake:
- Spent 10 minutes unsure about the invariant; started coding too early.

Next time:
- Always write window invariant as a comment before coding.

You can log these in your DSA learning path to track progress across multiple mock sessions.

Variations to Increase Difficulty Over Time

Variation 1: No LeetCode UI

Use:

• A simple text editor.
• A local test harness.
• No hints or “Run Code” button.

This trains you for onsite environments where you might not have full IDE support.

Variation 2: Verbal-only for the first 10 minutes

Force yourself to:

• Spend 10 minutes only on clarifying questions, examples, and approach.
• Only then begin coding.

This strengthens your communication and planning skills.

Variation 3: Multi-question sessions

Once comfortable:

• Do 2 problems back-to-back in 75–80 minutes.
• Simulate a real onsite round with short break in between.

Common Mistakes in Solo Mock Interviews

Mistake 1: Treating them like normal practice

If you pause the timer, peek at solutions, and casually debug for an hour, you’re not simulating an interview.

Fix: Protect the simulation: fixed timer, no editorial, strict rules.

Mistake 2: Skipping the retrospective

Without a quick review, you miss the chance to learn from the session.

Fix: Always spend 5 minutes after each mock writing a short note; tools like LeetCopilot can help you categorize your mistakes and suggest targeted follow-ups.

Mistake 3: Picking problems that are too hard

If you repeatedly get nowhere, you’ll just build frustration.

Fix: Choose problems slightly above your comfort level, not 3 levels higher. Use difficulty filters and curated lists.

Mistake 4: Ignoring behavioral aspects

Solo mock interviews are a great time to practice:

• Staying calm with failures.
• Explaining trade-offs.
• Owning mistakes instead of hiding them.

FAQ

Q1: How often should I run solo mock interviews?
1–2 sessions per week is plenty, especially if you also do normal practice. Closer to interviews, you can increase frequency slightly.

Q2: Should I always timebox strictly?
Yes during mock sessions. For pure learning/practice, you can relax the timer, but keep mocks realistic.

Q3: How do I pick good problems for solo mocks?
Use curated lists (Blind 75 / Grind 75), company-tagged problems, or see how to explain your thought process during coding interviews for interview guidance.

Q4: Can AI replace a human interviewer?
It can’t fully replicate human nuance, but tools like LeetCopilot can simulate interviewer behavior—asking follow-up questions, probing edge cases, and giving feedback on clarity—which is extremely useful between human mocks.

Q5: What if I freeze completely during a solo mock?
Treat it as data, not failure. Start your retrospective with: “Where did I freeze?” and adjust your prep plan (e.g., more work on pattern recognition or constraint analysis).

Conclusion

You don’t need a constant stream of human interviewers to get high-quality mock interview practice.

By combining LeetCode problems, a timer, and a structured routine—with occasional support from tools like mock interview simulator—you can build the exact skills real interviews require:

• Clear understanding, strong patterns, clean code, and calm debugging under pressure.

Make solo mock interviews a regular part of your prep, and the real thing will feel far less intimidating.