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44 lines
1.2 KiB
Python
44 lines
1.2 KiB
Python
"""Luhn Algorithm"""
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from __future__ import annotations
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def is_luhn(string: str) -> bool:
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"""
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Perform Luhn validation on an input string
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Algorithm:
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* Double every other digit starting from 2nd last digit.
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* Subtract 9 if number is greater than 9.
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* Sum the numbers
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*
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>>> test_cases = (79927398710, 79927398711, 79927398712, 79927398713,
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... 79927398714, 79927398715, 79927398716, 79927398717, 79927398718,
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... 79927398719)
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>>> [is_luhn(str(test_case)) for test_case in test_cases]
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[False, False, False, True, False, False, False, False, False, False]
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"""
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check_digit: int
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_vector: list[str] = list(string)
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__vector, check_digit = _vector[:-1], int(_vector[-1])
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vector: list[int] = [int(digit) for digit in __vector]
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vector.reverse()
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for i, digit in enumerate(vector):
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if i & 1 == 0:
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doubled: int = digit * 2
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if doubled > 9:
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doubled -= 9
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check_digit += doubled
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else:
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check_digit += digit
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return check_digit % 10 == 0
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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assert is_luhn("79927398713")
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assert not is_luhn("79927398714")
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