Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the mutation and copying bugs pattern
Assignment does not copy, a shallow copy still shares its contents, and mutating methods return None.
What went wrong: grid[:] makes a new outer list, but both lists hold the same rows. Changing a row changes it in both.
The fix: copy = [row[:] for row in grid]
Remember: [:] copies one level only. Lists inside lists need copying too, or use copy.deepcopy().
The pattern behind it: mutation and copying bugs.
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<iframe src="https://trybughunt.com/embed/b05f8775-6c90-421e-88ac-eed1f353da9f" title="Debugging challenge: Editing a copied grid changes the original" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe>
<p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/b05f8775-6c90-421e-88ac-eed1f353da9f">TryBugHunt</a></p>