checkdigit-barcode

Write best practice code in ruby to calculate the check digit of an ISBN13 barcode

The algorithm is:

1. Take each digit, from left to right and multiply them alternatively by 1 and 3
2. Sum those numbers
3. Take mod 10 of the summed figure
4. Subtract 10 and if the end number is 10, make it 0 Example for 978014300723:
5. (9×1) + (7×3) + (8×1) + (0×3) + (1×1) + (4×3) + (3×1) + (0×3) + (0×1) + (7×3) + (2×1) + (3×3)
6. 86
7. 86 mod 10 = 6
8. 10 - 6 = 4 Therefore the complete ISBN is: 9780143007234