October 25, 2019

The International Bank Account Number (IBAN) is an internationally agreed standard of identifying bank accounts with a hash number to reduce errors. The first two characters of an IBAN are the two-letter country code, the next two characters are a two-digit hash, and the remaining characters identify the bank routing number and depositor account number. For instance, here is a fictition British IBAN: GB82 WEST 1234 5698 7654 32. The full IBAN standard specifies the range of valid bank account numbers and depositor account numbers for each country; we are interested only in the hash code.

In the code shown above, the hash code consists of the two digits 82, which are validated as follows:

1) Move the first four characters from the beginning of the string to the end: WEST 1234 5698 7654 32GB 82.

2) Replace letters with two-digit numbers according to the scheme A = 10, …, Z = 35:
3214 2829 1234 5698 7654 3216 1182.

3) Treating the string as a large integer, divide by 97 and calculate the remainder.

4) If the remainder is not 1, the IBAN is not valid.

To generate a hash code, perform the same procedure as above with the two hash digits initially set to 00, then subtract the hash code from 98 and insert it in the IBAN.

Your task is to write functions to validate existing IBAN numbers and generate hash codes for new IBAN numbers. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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