File size: 323 Bytes
0981686 | 1 2 3 4 5 6 7 8 | Done. Created `fib.py` and verified with `python3 fib.py`.
**Results:**
- `fib(10) == 55` ✓
- Negative `n` raises `ValueError` ✓ (tested with `-1` and `-5`)
The function uses iteration with a two-variable loop, so it runs in O(n) time and O(1) space, and handles the edge cases `fib(0)==0` and `fib(1)==1` correctly.
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