42 lines
836 B
Python
42 lines
836 B
Python
#!/usr/bin/env python3
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"""Fibonacci sequence calculator."""
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def fibonacci(n: int) -> int:
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"""Return the nth Fibonacci number (0-indexed).
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fibonacci(0) = 0
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fibonacci(1) = 1
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fibonacci(2) = 1
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fibonacci(3) = 2
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...
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"""
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if n < 0:
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raise ValueError(f"n must be non-negative, got {n}")
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if n == 0:
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return 0
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if n == 1:
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return 1
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a, b = 0, 1
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for _ in range(2, n + 1):
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a, b = b, a + b
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return b
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if __name__ == "__main__":
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import sys
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if len(sys.argv) != 2:
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print(f"Usage: {sys.argv[0]} <n>")
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sys.exit(1)
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try:
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n = int(sys.argv[1])
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except ValueError:
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print(f"Error: '{sys.argv[1]}' is not a valid integer")
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sys.exit(1)
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result = fibonacci(n)
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print(f"fibonacci({n}) = {result}")
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