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95a4957d9e
* Luhn algorithm
Perform Luhn validation on input string
Algorithm:
* Double every other digit starting from 2nd last digit.
* Subtract 9 if number is greater than 9.
* Sum the numbers
https://en.wikipedia.org/wiki/Luhn_algorithm
* Update DIRECTORY.md
* Update luhn.py
* Update luhn.py
* Update luhn.py
* Update luhn.py
* Update DIRECTORY.md
47 lines
1.2 KiB
Python
47 lines
1.2 KiB
Python
""" Luhn Algorithm """
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from typing import List
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def is_luhn(string: str) -> bool:
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"""
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Perform Luhn validation on 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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>>> test_cases = list(map(str, test_cases))
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>>> list(map(is_luhn, 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] = [*map(int, __vector)]
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vector.reverse()
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for idx, i in enumerate(vector):
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if idx & 1 == 0:
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doubled: int = vector[idx] * 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 += i
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if (check_digit) % 10 == 0:
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return True
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return False
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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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