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You Use ChatGPT But Can't Explain Your Code in Interviews

5 min read
  • ai
  • interview
  • junior-developer

You solved the take-home with ChatGPT. The code ran. You submitted it feeling relieved.

Then the interviewer asked: "Walk me through why you chose this approach."

You froze.

Not because you are dumb. Because you had code without understanding, and interviews test the second thing.

If that sounds familiar, you are not alone. A growing group of junior developers can ship features with AI tools but struggle to explain variables, defend trade-offs, or debug when the prompt is not in the room. That gap is exactly what Prepzio is built to close.

Having code vs understanding code

There is a difference between:

  • Having code: a working snippet exists on your screen.
  • Understanding code: you can explain what each part does, what breaks if you change it, and how you would solve a similar problem tomorrow without help.

AI tools are incredible at the first. They are neutral on the second unless you do the thinking work.

Junior interviews, especially at startups and mid-size companies, rarely stop at "did it compile?" They want to hear you reason: Why a for loop here? Why not a map? What happens with an empty array? What would you log first when it fails?

If your learning loop is copy → paste → submit, you are optimising for demos, not hireability.

Five signs you might be AI-dependent

Honest self-check. You do not need to score perfectly; awareness is the point.

  1. You paste without reading. The answer lands in your editor and you run it. If it works, you move on. You cannot summarise what changed in your own words.

  2. You cannot explain variable names. An interviewer points at acc or result and asks what it holds at each step. You guess.

  3. You debug only by prompting. Errors become new ChatGPT messages, not hypotheses. You rarely form "maybe the index is off by one" before asking for a fix.

  4. The same problem fails the next day. Yesterday's solution worked. Today you face a slightly different input and you are stuck, because you memorised output, not pattern.

  5. Whiteboard panic. No autocomplete, no AI sidebar, no Stack Overflow tab. Your mind goes blank even on skills you "already did."

None of this means you should stop using AI. It means you are using it as a answer machine instead of a thinking partner.

Why LeetCode does not fix this

LeetCode optimises a different game: find the known pattern fast, implement cleanly, pass hidden tests.

That matters for some companies. But many junior roles, especially first jobs after bootcamp or self-study, weight communication, debugging, and basic system sense more than optimal Big-O on red-black trees.

You can grind 200 medium problems and still freeze when asked:

"You added this API call. What happens if the network is slow?"

Interview readiness for juniors is not only algorithm memory. It is explainability under mild pressure.

What actually helps (before you need it in a live interview)

You do not need a twelve-week plan. You need a repeatable habit:

Explain in your own words first

Before you paste anything, write two sentences: what the input is, what the output should be. If you cannot, AI will happily skip that step for you, and you will pay for it later.

Make a first attempt

Even bad pseudocode counts. A wrong loop with the right intent is more valuable than a perfect solution you cannot defend.

Use hints, not dumps

Good help sounds like: "Think about the last element you processed", not a full refactored file. Train yourself to ask for direction, then finish the thinking.

Reflect after every solve

Three questions, sixty seconds:

  • Why does this work?
  • What would break it?
  • How would I solve a neighbour problem (sorted → unsorted, array → string)?

That reflection is what moves knowledge from short-term paste buffer to long-term skill.

Where Prepzio fits

Prepzio is a practice coach for AI-using juniors, not another answer generator. In the private beta (summer 2026), you get short Socratic sessions: hint ladders instead of solution dumps, rubric feedback on how you think, and an Independence Score with levels L1–L5 framed as growth, not shame.

L1 looks like heavy paste-dependence. L5 looks like handling a fresh similar problem on your own. The goal is visible progress week over week, not hiding that you used ChatGPT yesterday.

If you want to measure that gap before your next interview round, join the waitlist below. First cohort gets beta access free and founder pricing if you subscribe later.

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