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106 lines
2.2 KiB
Markdown
106 lines
2.2 KiB
Markdown
---
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id: 6a0dcd03ee4e68698080ef6c
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title: "Challenge 308: Credit Card Validator"
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challengeType: 29
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dashedName: challenge-308
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---
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# --description--
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Given a string of digits for a credit card number, determine if it's a valid card number using the following method:
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- Starting from the second-to-last digit, double every other digit moving left.
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- If doubling a digit results in a number greater than 9, subtract 9.
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- Sum all the digits (doubled and undoubled).
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- If the total is divisible by 10, the number is valid.
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# --hints--
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`is_valid_card("4532015112830366")` should return `True`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("4532015112830366"), True)`)
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}})
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```
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`is_valid_card("5425233430109903")` should return `True`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("5425233430109903"), True)`)
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}})
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```
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`is_valid_card("371449635398431")` should return `True`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("371449635398431"), True)`)
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}})
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```
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`is_valid_card("6011111111111117")` should return `True`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("6011111111111117"), True)`)
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}})
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```
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`is_valid_card("4532015112830367")` should return `False`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("4532015112830367"), False)`)
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}})
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```
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`is_valid_card("1234567890123456")` should return `False`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("1234567890123456"), False)`)
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}})
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```
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`is_valid_card("4532015112830368")` should return `False`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertIs(is_valid_card("4532015112830368"), False)`)
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}})
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```
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# --seed--
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## --seed-contents--
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```py
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def is_valid_card(number):
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return number
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```
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# --solutions--
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```py
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def is_valid_card(number):
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total = 0
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for i, digit in enumerate(reversed(number)):
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d = int(digit)
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if i % 2 == 1:
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d *= 2
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if d > 9:
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d -= 9
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total += d
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return total % 10 == 0
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```
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