Luhn Algorithm

The Luhn algorithm is used to validate credit card numbers. The algorithm takes a string as input and does the following to validate the credit card number:

  • Ignore all spaces. Reject number with less than two digits.
  • Moving from right to left, double every second digit: for the number 1234, we double 3 and 1.
  • After doubling a digit, sum the digits. So doubling 7 becomes 14 which becomes 5.
  • Sum all the undoubled and doubled digits.
  • The credit card number is valid if the sum ends with 0.

Copy the following code to <https://play.rust-lang.org/> and implement the function:

1. // TODO: remove this when you're done with your implementation.
2. #![allow(unused_variables, dead_code)]

4. pub fn luhn(cc_number: &str) -> bool {
5. unimplemented!()
6. }

8. #[test]
9. fn test_non_digit_cc_number() {
10. assert!(!luhn("foo"));
11. }

13. #[test]
14. fn test_empty_cc_number() {
15. assert!(!luhn(""));
16. assert!(!luhn(" "));
17. assert!(!luhn("  "));
18. assert!(!luhn("    "));
19. }

21. #[test]
22. fn test_single_digit_cc_number() {
23. assert!(!luhn("0"));
24. }

26. #[test]
27. fn test_two_digit_cc_number() {
28. assert!(luhn(" 0 0 "));
29. }

31. #[test]
32. fn test_valid_cc_number() {
33. assert!(luhn("4263 9826 4026 9299"));
34. assert!(luhn("4539 3195 0343 6467"));
35. assert!(luhn("7992 7398 713"));
36. }

38. #[test]
39. fn test_invalid_cc_number() {
40. assert!(!luhn("4223 9826 4026 9299"));
41. assert!(!luhn("4539 3195 0343 6476"));
42. assert!(!luhn("8273 1232 7352 0569"));
43. }

45. #[allow(dead_code)]
46. fn main() {}