Does LeetCode Detect ChatGPT Code?

LeetCode is where many CS students practice for interviews, and its weekly and biweekly contests are a big part of that. With AI assistants able to solve many contest problems, the obvious question is whether LeetCode can tell. The honest answer is that LeetCode's official posts say AI tools are banned in contests and describe a cheating detection tool based on code similarity plus manual review. They do not describe a tool that recognizes AI-written code as such, and they do not publish any accuracy figures. The descriptions below come from LeetCode's official posts, which we read in October 2026.

The official contest rule

LeetCode's contest rule post (titled "New Contest Rule", marked as updated in September 2024) lists the actions it treats as contest violations. They include:

• one user submitting with multiple accounts during a contest,
• multiple accounts submitting similar code for the same problem,
• disturbing other users' participation,
• disclosing contest solutions publicly before the contest ends, and
• the use of code generation tools or any external assistance for solving problems.

The last item is the one about AI. The rule spells out that it includes putting problem statements, test cases or solution code into external assistance tools. That covers pasting a problem into ChatGPT, asking a chatbot to fix your failing code, or feeding it a test case you cannot pass.

The penalties

The same post lists two levels of penalty:

• First violation: contest score reset to zero, LeetCoins reset to zero, and a one-month ban from contests and discuss.
• Second violation: contest score reset to zero and permanent account deactivation without appeal.

LeetCode's May 2024 announcement on fairness in contests repeats these penalties and says they are applied without prior warnings and will not be waived for any reason.

How LeetCode says it detects cheating

The announcement says LeetCode's advanced cheating detection tool identifies similar codes, and that the team conducts manual reviews to confirm any dishonest behavior. It also asks users to report suspected cheating to support, says the team reviews those reports, and says it tries to ban cheaters before rankings are finalized.

That is the full extent of what the official posts say about detection. In particular, they do not say:

• that LeetCode runs an AI-text or AI-code classifier,
• which signals the detection tool uses beyond code similarity, or
• how often it is right or wrong.

Anything more specific you read online, such as claims about typing analysis or exact thresholds, is not something we could find in LeetCode's own documentation.

Why similarity still matters for AI

A similarity tool does not need to know about AI to catch some AI use. When many people paste the same contest problem into the same assistant, the answers can come back with closely matching structure, and the rule already treats multiple accounts submitting similar code as a violation. Then a person reviews the match. A similarity check cannot say where the code came from, though. If you want to understand that limitation in more depth, see does MOSS detect AI-generated code, which covers the same idea for classroom tools.

Contests versus practice

The rule is written for contests. We did not find an official LeetCode rule that forbids AI help on regular practice problems, so we will not claim one exists. But it is worth being honest with yourself about what practice is for. Interviewers ask you to explain your approach, handle a follow-up, or change the solution on the spot. If an assistant wrote the answer, you have practiced reading code, not solving problems. Using AI to explain a solution after you have tried, or to check your understanding of an algorithm, is very different from letting it solve the problem for you.

If you think you were wrongly flagged

The announcement says that if you believe you were banned by mistake, you can contact support@leetcode.com, and that they may ask you to present evidence or provide explanations. Write a clear, calm explanation of how you solved the problem: the idea you started from, what you tried, why your code looks the way it does. Standard problems often have one natural solution, so two people writing similar code independently is not unusual. Our guide my code was flagged as AI but I wrote it has more on preparing that kind of explanation.

What this means for you

• In a contest, do not use AI. The rule is explicit and the penalties are serious.
• Read the current rule before each contest. The posts describe similarity checks, manual review and user reports, and the rules can change.
• In practice, use AI in a way that builds skill. Try first, then ask for an explanation, then rewrite the solution yourself from memory.

Checking how your code reads

The detector at the top of this page is not LeetCode's tool and does not tell you what LeetCode will do. It looks at style patterns people often associate with AI output, such as comments on every line or extra demo code. If you are curious how your own practice solutions read, paste one in and look at the reasons it gives. For the broader set of signs, see how to tell if code was written by ChatGPT.

Read more

• My code was flagged as AI but I wrote it — what to do after a flag.
• Does MOSS detect AI-generated code? — how similarity tools work.
• Can professors tell if you used ChatGPT for code? — the classroom side.

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