FA-72422 / Check-digit algorithms / Member archive

ISBN-10 weights start at nine · case 02

Correct ISBNs are rejected and some typos are accepted.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

ISBN-10 validation. Hyphens and spaces are removed; the rest must be nine ASCII digits followed by a digit or uppercase X (value 10), else "malformed". Weights run 10 down to 1 from the left and the number is "valid" when the weighted sum is divisible by 11, else "invalid".

Why this case matters

Catalogue and bookstore systems validate legacy ISBN-10 identifiers on intake.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression ["9379774826"]	`"invalid"`	`"valid"`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.