Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the logic errors pattern
The wrong operator, an inverted condition, a formula the right way round but backwards.
What went wrong: the loop visits every copy of 2, and each one passes the check, so 2 is added twice.
The fix: if nums.count(n) > 1 and n not in dups: dups.append(n)
Remember: "is this a duplicate?" and "have I already listed it?" are different questions.
The pattern behind it: logic errors.
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<iframe src="https://trybughunt.com/embed/905e9bd1-89c6-4b43-aca7-35be55fe6553" title="Debugging challenge: Duplicate finder reports each duplicate twice" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe>
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