ISBN13 check digit
Validate the check digit of an ISBN-13 code. Use some good and bad codes of your choosing for testing.
You are encouraged to solve this task according to the task description, using any language you may know.
- Task
Multiply every other digit by 3. Add the digits together. Take the remainder of division by 10. If it is 0, the ISBN-13 check digit is correct.
- See also
See https://isbn-information.com/the-13-digit-isbn.html for details on the method of validation.
langur
<lang langur>val .isbn13checkdigit = f(.n) {
val .s = replace(.n, "-", "")
if len(.s) != 13 {
return false
}
# multiply every other number by 3
val .nums = map(
f(.i, .d) if(.i rem 2 == 0: .d x 3; .d),
series(13),
map f .c-'0', s2cp .s,
)
fold(f .x + .y, .nums) rem 10 == 0
}
val .tests = h{
"978-1734314502": true, "978-1734314509": false, "978-1788399081": true, "978-1788399083": false,
}
for .key in sort(keys .tests) {
val .pass = .isbn13checkdigit(.key) write .key, ": ", if(.pass: "good"; "bad") writeln if(.pass == .tests[.key]: ""; " (ISBN-13 CHECK DIGIT TEST FAILED)")
}</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad