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36 lines
913 B
Markdown
36 lines
913 B
Markdown
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# Luhn Algorithm
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The [Luhn algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) is used to
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validate credit card numbers. The algorithm takes a string as input and does the
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following to validate the credit card number:
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* Ignore all spaces. Reject number with less than two digits.
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* Moving from right to left, double every second digit: for the number `1234`,
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we double `3` and `1`.
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* After doubling a digit, sum the digits. So doubling `7` becomes `14` which
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becomes `5`.
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* Sum all the undoubled and doubled digits.
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* The credit card number is valid if the sum is ends with `0`.
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Copy the following code to <https://play.rust-lang.org/> and implement the
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function:
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```rust
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// TODO: remove this when you're done with your implementation.
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#![allow(unused_variables, dead_code)]
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{{#include luhn.rs:luhn}}
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unimplemented!()
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}
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{{#include luhn.rs:unit-tests}}
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#[allow(dead_code)]
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fn main() {}
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```
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