Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the off-by-one errors pattern
The loop that runs one time too many, the slice that drops the last item, the index that starts in the wrong place.
What went wrong: range(1, n) gives 1, 2 … n - 1. It stops one number early, so n is never added.
The fix: for i in range(1, n + 1):
Remember: in range(start, stop), the stop number is never included.
The pattern behind it: off-by-one errors.
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<iframe src="https://trybughunt.com/embed/0f6dd197-9089-4623-996a-a8ffa986f9ff" title="Debugging challenge: Sum from 1 to n leaves out n" 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/0f6dd197-9089-4623-996a-a8ffa986f9ff">TryBugHunt</a></p>