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0cae02451a
* Added nth_sgonal_num.py * Update and rename nth_sgonal_num.py to polygonal_numbers.py --------- Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>
33 lines
914 B
Python
33 lines
914 B
Python
def polygonal_num(num: int, sides: int) -> int:
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"""
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Returns the `num`th `sides`-gonal number. It is assumed that `num` >= 0 and
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`sides` >= 3 (see for reference https://en.wikipedia.org/wiki/Polygonal_number).
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>>> polygonal_num(0, 3)
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0
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>>> polygonal_num(3, 3)
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6
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>>> polygonal_num(5, 4)
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25
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>>> polygonal_num(2, 5)
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5
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>>> polygonal_num(-1, 0)
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Traceback (most recent call last):
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...
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ValueError: Invalid input: num must be >= 0 and sides must be >= 3.
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>>> polygonal_num(0, 2)
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Traceback (most recent call last):
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...
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ValueError: Invalid input: num must be >= 0 and sides must be >= 3.
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"""
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if num < 0 or sides < 3:
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raise ValueError("Invalid input: num must be >= 0 and sides must be >= 3.")
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return ((sides - 2) * num**2 - (sides - 4) * num) // 2
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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