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36 lines
662 B
Python
36 lines
662 B
Python
#!/bin/python
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"""
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Write a function fib() that takes an integer nn and returns the nnth Fibonacci number.
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"""
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# this is O(2^n)
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def fib(n):
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if n in [1, 0]:
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return n
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return fib(n - 1) + fib(n - 2)
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print fib(10)
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# this is O(n)
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def fib(n):
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if n < 0:
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raise ValueError('Index was negative. No such thing as a '
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'negative index in a series.')
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elif n in [0, 1]:
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return n
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prev_prev = 0 # 0th fibonacci
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prev = 1 # 1st fibonacci
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for _ in range(n - 1):
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current = prev + prev_prev
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prev_prev = prev
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prev = current
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return current
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print fib(10) |